You do a lot of searching on the internet and military vehicle magazines, talk to people in the MV collecting field, follow up on every lead, and be persistent. The process can take years. Luck plays a big part in it, unfortunately.
There are perhaps twenty V100's known to be in private hands within the US. There are far fewer V150's and Dragoons. Two very nice restored V100's changed hands within the last year, neither went cheap.
Parts are just as much fun to track down. Helps to have, or know folks with, mad fabrication skills, because you are going to hand make a LOT of pieces! Parts for my V100 came from as close as a local junkyard, and as far away as Saigon (NOS traverse lock pins, enough to go into three ongoing restoration vehicles).
Cheers