Trying to find all companions in ME3

First thing to make sure of in this case is that all of your team from ME2 survived the Suicide Mission.

^Not really, ony Tali and Garrus need to survive.

I still haven't figured out how to get to Tali. Is that after the Citadel attack? Everybody survived the suicide mission in ME2. I really wish primary and secondary missions had been kept separated in ME3 like they were in 2. Im trying to do Citadel: Barla Von and I can't finish it because I have already scanned the planet once.

I looked up Tali and looks like she's a bit after the Citadel attack.

Complete ALL me2 missions, ALL me3 missions and play Citadel DLC before Act III.
I think Tali will be available after Priority: Rannoch, if she survive

In order for squadmates or other NPCs to become available you must complete their full story arc in the main game. For example, Jack isn't available until you've met her at Purgatory after the Grissom Academy mission. More details here: http://masseffect.wikia.com/wiki/Citadel:_Party#Preparation