Reachmahjong.com

(Forum topic #1000)
I guess you can call this a game although it seems like more of a practice.
Found this app (IOS) where you try to pick all the tiles that would give you chinitsu.
It can be harder than it looks, especially if there are multiple tiles that do it.

The above is similar to another app (IOS) called Flush Mahjong, which is more of a game.
A variation of this (with 2 suits) was mentioned previously by Ozball. viewtopic.php?f=3&t=53213#p56718

Yes, flush waits can be a headache!

This browser-based head-to-head flush game has been posted previously: http://www.gamedesign.jp/flash/bamboo/bamboo.html

I just got Renhou and Chiihou.

This is on the same site that has excellent free online mahjong, shogi and koi-koi games with an English interface.

http://www.gamedesign.jp/flash/mahjong/mahjong_e.html
http://www.gamedesign.jp/flash/shogi/shogi_e.html
http://www.gamedesign.jp/flash/hanafuda/hanafuda_e.html