I don't know of any other dedicated directadmin forums. Only hosting forums which also sometimes give answers to questions about panels.
We got a good one here, called Zeiter, which on his site has some very nice docs pointed to (on Poralix dot com).
But for support and questions about Directadmin, this is the place to be if one is admin or reseller. Not really for endpoint customers.
This forum has people like Brent (above) and sometimes me too, which help people where they can. And there are several others too. I started with hosting almost 13 years ago and never encountered a better place for DA questions.