The 'homeworld' aspect is really just a rule mechanic to accommodate pre-career (18 year old) skills. Its a good mechanic, but a shortsighted choice of terminology.
By the term, one logically would assume the need to pick a world, determine Trade codes and take (and pick) skills. Hence, the book says that the 'world' can be picked later.
However, as really just a collection of trade codes related to the PCs history, 'homeworld' really wouldn't have to be a specific system/planet. A PC could be born on a particular world and then immediately moved, etc. A better term would have been 'Pre-career Skills' or some such.
A PC could have been born and raised in a system or on a world, moon, space habitat, or even spaceship (maybe they are a Gypsy) or any combination of such. In some settings (the plain cover books are 'supposed' to be setting independent), one might want to record citizenship, etc.
Anyway, if you want to record an actual 'homeworld' in the 'Third Imperium' (3I) or any other system in the Official Traveller Universe (OTU) your best source online is probably www.travellermap.com - you can even search by Universal World Profile (UWP). To do this, simply specifying a search query of XXXXXXX-X (seven alphanumeric characters, hyphen, one alphanumeric character), or use uwp: in front of the code (you can use * and ? wildcards).
Bear in mind, travellermap does not match the Mongoose Traveller (MgT) 3I books exactly (MgT has changed some UWPs in their handful of sector books).
Have Fun!