Asteroid bases tned to be of two types, covert military ones where they are using the asteroid to hide in, and commercial ones (belter sites etc.) because asteroids are cheap. There is an asteroid city in one of the gurps JTAS mags. There are underground cities in Alien realms and the big traveller adventure - they are similar to an asteroid city.
I have used an asteroid base as a covert base for solomani raiders in the rebellion era.
As for maps - There is a issue of challenge with a TNE adventure that has a small covert asteroid base (a hideaway to get to the new era. Beltstrike, and Fate of the skyraiders are good sources. There has been a few in challenge, and some of the starwars adventures (both in challenge and the proper ones had asteroid bases).
Cheers
Richard