There's a way to help you re purchase ps3/ps4 avatar atm but i dont think there's a way to purchase avatar from different region to your current region account. Those stuff are not sharing between accounts, even if you create a JP ps account and purchase the avatar you still wont able to use them on your US account.
Well they did allow you to use custom avatar as profile picture tho, maybe you can alter it and put them as your profile avatar (but only you and close friend able to see the custom profile avatar you set)
