Actually, I think the crux of a successful resistance movement, given the circumstance is science. To be specific, rocket science.
No, I'm not kidding.
By TL8/9 ... it's actually difficult but not impossible for a civilization to get a rocket into orbit. It's also useful for much shorter-ranged rockets. Of course, you can put an explosive warhead on a rocket and it becomes a weapon. If you put a guidance system on the rocket, it becomes a missile. Various militant groups in the Gaza Strip are able to make their own (primitive) anti-tank rockets and that's with a shoestring technology level probably around TL5 or TL6. At TL8/9 everything we're building in "first world" countries is possible.
In our own modern world (which is arguably TL8/9 in many areas), only a handful of countries on Earth have the capacity of getting rockets into orbit reliably since it takes time to develop the expertise that goes along with the technology to get stuff into orbit. However, in a world where TL8/9 exists on a colony because it is below the median technology level of the universe, more reliable rocketry technology might exist as a turnkey solution for various purposes.
Given widespread support in the cities where industry exists, rocket parts could be made surreptitiously. From there, it'll be necessary to test the rocket engines and build a launch base and so on. Now, many of you reading this, with the idealized 21st century view of technology would pretty quickly deem it impossible given the realities Remote-Piloted Vehicles and Orbital Reconnaissance. I'd agree that in theory that's true. In practice, I think it's a very different ball-game. A colony of 500,000, mostly in the cities. Assuming the world is about the size of Earth, that's 500,000 people living in total on Earth, concentrated primarily in cities. Depending on the pattern of settlement, it's not inconceivable that an entire hemisphere is totally uninhabited. Even if the cities are spread out over the world equidistantly (for whatever reason), it still leaves vast tracts of the world pretty much uninhabited. This is important, since the occupation forces basically have zero interest in anywhere that their subject peoples don't live. It's "practical" for the occupier who can be assumed to have limited resources.
So here's my proposal: Assuming that the occupation forces, even using electronic surveillance and other force multipliers still cannot totally lock down the cities. Sympathetic native police can probably be persuaded to look the other way. An estimated number of people, say about 50 with the proper mix of scientific and technical skills need to be smuggled out of the city. My proposal would be to set a fire and fake their deaths, at a chemical refinery. It's important to make it look like this is an accident as opposed to terrorism/resistance. Given the high heat, many bodies will never be found, of course.
These people would be smuggled out of the city, with the rest of the support drawn from outlying farming communities (where it can be assumed that control of the population is probably not as tight). These farmer types are important as they'd have the skills to navigate and operate off-road vehicles or boats. This team would go and out and set up the hidden bunker complex the most extremely remote area of the world (as far as human settlement goes) for the facilities to test rocket engines, do small test launches and so on. Ideally the rocket engines and similar materials could be clandestinely made in the cities and shipped out.
Once this ground-based ad-hoc surface-to-orbit missile is viable, they can move to mass production, as much as they can manage, and start creeping their launching sites back towards civilization. The point is to start denying as much of low orbit to spacecraft as possible. While a full modern space fleet would laugh at such primitive missiles, chances are State B is not going to have such modern warships that are sorely needed elsewhere. Chances are there's only going to be a single warship or a few second or third line warships, probably in the "gunboat" or "frigate" range. And long before then, these missiles will be able to knock spy satellites out of orbit. What the missiles might lack in modern technology can be made up using swarm attacks of many missiles. Shooting down or heavily damaging the single naval warship, and showing the world has the capacity to keep building such missiles at a high rate is going to be pretty discouraging to a military that could use such expensive, difficult to replace warships elsewhere. Such missiles can also threaten the fat, slow, poorly defended freighters that come to pick up the refined metals.
Such missiles can also be used as ballistic missiles. If things like orbital catapults are used to get the metals into orbit, they can be used to bombard the catapult site. Same story for a spaceplane field. Shorter ranged rockets can be used to shoot down things such as RPVs and jet fighters, and helicopters (all likely, given the desire of the mining corporation to keep things cheap). More high-tech front-line fighters might be detailed, but even primitive missiles will get lucky and a missile with a 5% chance of hitting is going to scare fighter pilots when the resistance can fire them twenty at time...
EDIT: I should add before someone asks "how are you going to get guidance in there" that it's important to remember when you have a large portion of the technical, civilian population at least passively helping you, many technologies that seem harmless to an occupier can be repurposed. For instance, a modern infra-red security system, the type that is used to both check for fires as well as keep watch for intruders is a pretty discerning system. It's not that difficult to retask such technology to make a missile seeker that could differentiate between the hot radiator fins of a fusion reactor aboard a starship or the jet exhaust of a fighter and that of a distraction flare or the sun. The RADAR that the police use to track speeding vehicles is in theory not too hard to scale up shoot hypervelocity "dumb" missiles useful to shoot down aircraft with good countermeasures.
