I did a google search for webchat on the undernet... found a few that are independent of www.undernet.org. Incidently, I used the second one a few days ago to try something out and it worked fine for me. Hope one of these works for you.
There's a German site which, if you don't know German, you can probably fumble your way around anyway.
Or there's this site from Blue Yonder. This is the one I used without any difficulties.