If you're looking for arcade PCBs, make sure you go there the Surugaya next to Beep. There are several surugaya locations now.Mak, Beep, G-Front and Suruguya are worth visiting for sure
Probably KVC Lab (link)? Also sells infinikeys for CPS2 if you need some.There’s another PCB store in Akihabara that opened but the name escapes me