I have downloaded a handful of modded factions and I've noticed a handful of them don't appear on the scroll down selection list on campaign. For example Bear-faction doesn't appear in the scroll down selection list yet Crobotech does. It's a little annoying because in that case, you have to play as another faction for example Dummies and then go into the buy menu, which is the only way to spawn them in campaign. Could anyone give me some help to how I can put them in the selection list for campaign?

Just add 'Tech' at the end of the faction name in the index.ini file.

For example, Bear Federation Tech would be what should appear in the index.

Or.. You could look at this thread
viewtopic.php?f=1&t=31031