Especially during the weekend, you’ll find all kind of events going on and in Japan they love to dress up for the occasion! Now that Harajuku bridge is no longer the place to see cosplayers, Akihabara is the place to be. The Maids don’t usually want to have their photo taken, but “booth babes” at events, are usually ok with it. Always ask their permission though :) If you want to buy some Cosplay yourself, you can visit several shops like:
Mandarake: Second hand, but perfect quality costumes, wigs and props.
Don Quijote: Cheap, not the best quality, but good enough to wear at least a few times. Don quote can be found everywhere around Tokyo, but the one in Akihabara gives you the biggest selection.
Cospa: Huge selection of new and second hand cosplay, wigs, shoes and props.
ACOS Akihabara: New costumes, wigs and props. Not the biggest store, but still a fairly good selection of all kinds of Cosplay.