There's a modified version of Tetr.js, which has an "Arika*" rotation system (it's basically just Ti's ARS) in its settings. It's not really TGM, even with the "Arika*" rotation system, but at least you can practice playing with custom controls.
That looks like an outdated mirror of farter's fork of tetr.js (http://farter.cn/tetr.js). The original has a few extra modes and rotation systems now. Dr-Ocelot's fork has a Grades mode that seems to be trying to replicate TGM, that might be worth looking at as well.
