[quote name='Brak']Like orntar said: Just finish the Carnales story-arch. Your homies will drive "tricked out" Bulldog's all over town.[/QUOTE]
Actually, I don't think it's finishing the Carnales... the more territories you accquire gets your homies to drive better and better vehicles and have better guns.
I just finished the chop shop at the end of the game because they were all driving Bulldogs then. Never saw one any other time.
Also, go do the Hijacking at the airport, level 7 you get to hijack a bulldog. When you get it, cancel the mission, go to the forgive and forget to get rid of the cops, and drop it off.
Also, the Bulldog dosen't show up at Museum for some reason, I searched there for hours once and it never showed.