If you're looking for airsoft stuff, then there's quite a few shops in/around Kyoto, it all depends on what style of play. There are shops that specialize ONLY in guns that fire over 400fps and shops that specialize ONLY in guns that shoot under 400fps.
Other than that, check out a Tokyu Department store and look in/around the toy section to find TONS of TM springers of all shapes and sizes (hahaha, in Japan, springers are considered toys, what are they considered here... PROHIBITED WEAPONS... WTF?)