The "Golden Dawn" orders active today stem from a re-make established according to Regardie's papers, so none actually continue the Mathers/Westcott lineage.

Mathers was something of a huckster himself, so that might not be bad. Your best bet, from my perspective, is the David Griffin order. He has some personal problems, but the order is well-organized and you ought to have a chance at participating.

Avoid anyone offering "astral" participation.

Wondering what's involved? Well, what you see is what you get. It's not a secret order, just a private one.