ASC for learning about parts and names.
Anywhere really for upgrade parts. You can import those so go nuts. Obviously parts that are prohibited you'll have to get in country but things like Mechboxes, springs, pistons, etc. should make it through the border. The "standard" sites I've heard about are places like airsoftparts, Redwolf, Den, WGC, War4, UN Company, etc.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE