So, there's nothing wrong licensing-wise with this sort of thing? I'm glad, because I found the Teespring shirt independently (http://teespring.com/macsbrownbottle), ordered one, and then saw someone else wearing one at our local RenFest last weekend! (In fact, I just joined the forums so that I could look to see if I should be sending his agent five bucks or something. )
There is a problem, but until Jim, his agent, and I can sort out how to satisfy fan demand without stepping on anybody's fun, we're kind of looking the other way. It's a source of major stress in my life when I see folks selling their designs, because I want to say something, but I don't know what.
My current favorite idea is to hold periodic t-shirt contests to get new designs added to the official store, with profits split between the creator and Jim, but that would require Fred or me to have the time to run said contests.
Another option might be for folks to seek out Jim's approval to sell their designs (as GillyPerkyGoth did), maybe with a special graphic to indicate to buyers that they have permission and an honor system that a certain percentage of their profits be donated to a charity of Jim's choice.
We want to preserve the power of Jim's copyright, but we also don't want to alienate fans who just want to show their love of the series. Any suggestions for how to do so are welcome!
If you're looking to compensate Jim or his agent, I suggest you make a donation to Jim's favorite charity,
Missouri Pit Bull Rescue.