You probably should have gotten your labels before you ordered your shirts.
If you had done that, you could have sent your labels to TSC Apparel, bought your shirts from them, and had them place your labels in before they shipped the shirts to you.
Then you would have had 300 AA shirts with your label ready to get printed.
If your shirts are already going to be printed by a printer, you now have to get your labels made, and have your very expensive shirts (because now they're printed!) handled by someone to place your labels in them. Unless you find a printer that will do it for you.
Are the shirts already at the printer's?
Do you have the blanks now?
Are you buying the shirts through the printer?
A little more info on where everything stands will help.
