Hi there!!! I agree that smartstim is a great place for info.
A couple of online manufacturing sites are:
erostek.com
I actually have the ET 232 and it is a great unit.
However, the key to great e stim play are also the electrodes and PES make amazing electrodes. There site is:
peselectro.com
They are based in Las Vegas and I happen to be going there later this week. I am shopping for a few new electrodes and can't wait to try them out!