The TrotMania IRC channel is #trotmania on Canternet. You can either join manually with your favorite client (we know you have one, admit it. Liro uses Hexchat) or use this web chat.
If you want general StepMania support, you can either go to the StepMania website, or the StepMania IRC channel (#stepmania-devs on Freenode. They have a very similar web chat client too)