The usual method of printing on t-shirts is screen printing. Just google "screen printers in [your area]" - call one, and get a quote. They should also be able to help you prepare your artwork, or they might even do it for you. It's unlikely that they will be able to use the image you made in Photoshop directly. You'd need to provide separations for screen printing, so they can make an individual screen for each colour.
I think it is better to consult and hand printing worker, for make the print on your shirt, he will help you with the best model that you give, otherwise consider any printing service provider with a machine. Choose any one, which you feel best.