If anyone can help me with a situation I'm in. I want to support this artist and buy his work. I can get it for free, but I can totes afford to spend a couple bucks on him.

Anyways, I've been trying to go through pixiv and other purchase service sites, but I can't seem to find guides or help to actually use an American card to buy from Jap sites. Can anyone direct or help me please? Any help is much appreciated.