Reachmahjong.com

I think there is now a way to purchase kaimo for Janryumon for those of us outside of Japan.

However, I do not believe that non-Japan (at least those from the USA) credit cards will be accepted by the system, since I've tried both of my cards and got the error "this card cannot be used."

However, if you have access to something like WebMoney, BitCash or NetCash, they may work out better.

Webmoney was always accepted from outside Japan. You just had to use a fake postal code/address from the internet.

Source: I won a 300 people JRM league where the prize was 2000 webmoney (2000 JPY), and spent it promptly on Janryumon 2. It seemed fitting to spend the money won from the tool in the tool. Almost poetic.