Hi Longbow, I go to a couple shooting forums and have also benefited from the group buy thing. I'm currently on a group buy at castboolits for a 9.3 bullet mold...
As for archery related stuff, might be a little harder to swing. Bows being the individual things they are, most guys want to personalize them but I could see something like a Tradgang Limited Edition of "Bow ______" being something that a lot of guys might be interested in. Maybe something easier might be a group buy on broadheads where the "group" might buy say a hundred or more heads and get a slight discount or maybe have some bow cases with the trad gang logo on them. Problem is, the use of the logo would be up to the site and they might prefer to offer a line of merchandise themselves rather than allow their name to be put on a private run of stuff. Of course, if you could get Black Widow or ACS or somebody like that to do a limited run of almost any bow even without the tradgang logo I bet you'd get some takers.
I bet there's a way to do something though.