Depending which area you live, there is one in China Court, I.B. or Sweet Surprises party shop in the road opposite Lulu. Pretty sure there is one in Mercato as well.
<em>edited by amelia on 24/06/2012</em>
I don't know if this will help, but I recently ran into an old friend of mine who started an online t-shirt printing business here in Dubai. I picked up his card, and he has a website as well. His company is Ink Mash, and his number is 04-4486268. Website is www.inkmash.com. Maybe he can help.