What you're not allowed to import:
- Complete guns
- lower or upper receivers (depending on where the serial # is on the real steel)
- pistol frames
- grenade lanchers & shells
- any magazine with fake bullets
- sound supressors
I THINK that's if, but may be forgetting something. Anyway, that's a pretty good list of what you can't bring in.
List your gear as paintball equipment, and pack the BBs separately from that stuff, and you're good to go.