Mooseslayer

Veronica is at the 188 Trading Post. 
Boone can be found in the head of the Dinosaur in Novac after 9PM. You have to complete a mission for him before he can be your companion. 
Rex is at the King's School of Impersonation. 
Cass is at the bar at the Mohave Outpost. You've probably walked right by her already during an earlier mission.
Other places to find companions are Jacobstown, Black Mountain & the Old Mormon Fort.

84) Fighting Matthew Perry  to the death in an arena armed only with machetes is so satisfying

Quite impressive, but I think I'd make it halfway through a play through, get impatient and shoot someone's head off

Awesome