'Slugthrowers' are not impossible to get on station, Garobaldi had one, "Grey 17 is missing".
Not impossible, just illegal.
And some types of ammo will be even more illegal (armor-piercing, since that's most dangerous, decompression-wise)
One of the things about PPG's is that they fire shots "made of heat". Burns right through organics at a high setting, but when it hits a plasteel wall it just heats the wall (note to characters - don't touch the spot where a PPG blast has hit, or you'll burn your fingers). You need multiple shots to get the metal of a bulkhead to start melting - depending on how thick a bulkhead, many shots. And that's why they`re relatively safe on board a spaceship/station.
So any human who has the neccessary connections, or a plausible cause, can get a permit for a civilian Wesson&Grumman PPG.
Same for aliens - Ta`Lon has his sword (he was an official bodyguard, certified by the then centauri-controlled narn regime), the Centauri Royal Guards had their daggers and PPG's, et cetera.
But noone would get an official permit to carry a slugthrower - because a solid slug has more penetration then a blast of a few super-heated helium molecules. It's not only decompression when a stray shot hits a thin part of the outer hull, or a window, it's also the danger of going through a wall and damaging the stuff that's behind it - tubes and wires that power the machinery the ship/station needs to function (remember, spoace is a very hostile place unless you have machines working on giving you air to breathe, warmth to live etc.)
I suppose, if you have Really good connections you can get around that too. Especially when it concerns "museum pieces" (which may be officialy "non-firing" - like in "firing pin removed", something that could easily be fixed by a competent gunsmith). Remember, Garibaldy never used the gun, he just had the live bullets...
So, if players are employees of a private security firm... it depends on the firm in question. They might get permits for civilian firearms... or they might not, and be told to use non-lethal weaponry only. Stun batons, tasers, foam launchers, whatever. I suppose it will depend on the type of security the firm offers (or what deal they can make with station security!) GM call - what do YOU want? :wink: