There is an online company called Mrcloud who produce Mii shirts.
Add their friend code, send your Mii, pay some money, 1 week later a lovely T-shirt arrives.............. or so they say.
One month ago they took my cash and still no Mii-shirt. I tried to contact them by a variety of methods and they failed to respond until I threatened to bad mouth them over the net.....
They sent me an email which I replied to over a week ago and STILL NO MII-SHIRT. Ngamer mag are praising them but my honest advice is DON'T USE THEM