sadly when I was there I didn't have enough time to visit echigoya in shinjuku or akihabara, even though I was probably less than a block away from the shinjuku store, I didn't know it was there until I returned to the hotel and didn't have time to go back.
Gear is super expensive there, I did find some surplus and costuming stores, they wanted something like 4200y for a basic condor belt, which you can get here for about 20 bucks. 4200y for those not keeping track is about 45$. I didn't trip over any airsoft specific stores either, but in terms of what you can get, it's probably all TM.
Taxes and levies on anything non domestic made are apparently quite high which are reflected in the price.
Hard to do everything you want and see all you want to see in just 2 weeks.. especially my 4 city schedule... all the more reason to go back.