Sign up with TSF Sportswear to buy the blanks and then use a contract screen printer. TSF has a warehouse in Pompano plus several others around the country.
I personally use Seaside Graphics in Pompano Beach. Steve only does work for the trade and his prices are really hard to beat. You can order the shirts, have them shipped to Seaside and then Steve will UPS the finished product to you. He does not have a fancy website or anything, strictly old school but a great guy to work with.