Making samples, and then submitting them to FASA is probably the best idea. Either way, you get some SR gear. And maybe, just maybe, you get them to market it.
However, due to the relatively limited market, items that non SR's would buy just beccause it "looks cool" would have the best chance.
Tshirts are easy. Buy a pack of the special paper(usually comes with software), print up what you want, iron it on.
Mugs are tougher, but not undoable. If you can get what you want into a picture format, or something the Walmart Photo Center can use, you can purchase a photo mug for about 12 dollars. Or, go to a pottery painting place and paint your own. Around here, that would cause me probably $15-$20, but it's worth it for that extra cool look. A modicum of artistic talent is necessary.
My poor husband, now he gets to help me make a mug!
But he won't mind so long as he gets a GM of doom mug.