There are full instructions on the following webpage including a link to Kotaku's guide to registering for the Japanese PSN. There are also two links to the full catalogue of titles available - the first one is for mostly PS3/Vita games and other is for mostly vintage PS1 games playable on current consoles.
http://www.dualshockers.com/2013/06/22/ ... tion-plus/
The selection includes the following four PS1 mahjong games:
https://store.sonyentertainmentnetwork. ... 0000000001
https://store.sonyentertainmentnetwork. ... 0000000001
https://store.sonyentertainmentnetwork. ... 0000000001
https://store.sonyentertainmentnetwork. ... 0000000001
I've got about a dozen games downloading right now.
