Rich, you've probably already considered this, but I have had great luck getting things sponsored in the past. IF you'll be accepting advertising on TFL someday, perhaps there's a company or two (or ten) who would just love to help us with the t-shirts. TFL logo on the front, advertising on the back? Perhaps a slogan on the front 'TheFiringLine.Com - take your best shot!' or some other cute / clever eyecatcher, with your graphic in the middle of the back and surrounded by company logos for H&K, Sig, Glock, Busmaster, Colt, Para-Ord and so on. For those companies this would take a miniscule investment.
It would be a pain in the a** for you, but ATM's idea could work as well. On the other hand, perhaps a t-shirt company you could trust would handle the admin?
Whatever you decide, don't take on this additional brain damage if it doesn't fit with your plans for TFL. The last thing any of us want to see is for you to get discouraged with this site. You and your crew have created a very special meeting place here. Thanks again.