Depends on the era you're playing with really.
The
MUL can show you what ComStar has available to it over the years. If you want more generic stuff, you can add "Inner Sphere General" to the faction filter.
Prior to Tukayyid, they're going to be able to pretty much have whatever they want, such as old Star League tech that they've saved, and buying anything else over the centuries, except for late bloomers like the Wolfhound. After Tukayyid, they're going to still have the Star League tech, but they're also buying from mostly Kurita, and the FedCom after that.