where can i buy japanese used phone cards

Do you know where i can buy Japanese used phone cards in Tokyo or in Japan coz i'm collecting theim
thanks for your help

Look for coin and stamp shops in department stores. They will be in or near the toy section.

Coin shops for hobby collection purpose sell them but used phone cards are less demand these days so you may find difficulties to find suitable shops you want.
There are still brand new phone cards available at those shops for your collection.

Thank you very much for the advice
i hope i could find some cards there

Mandarake in Akihabara (perhaps in the Shibuya store too) has some used / collector phone cards. I think it's in the same section as their trading card games (behind glass) near one of the top floors. I didn't pay much attention but I did see some of what you're looking for while passing by.