I have had luck with some of the Omni Wick columbia t-shirts they are a cotton poly blend.I am not sure if the bulk order. Merino would be great but the price is a killer.
The second round shirts are on hold until Summit will go to lunch with me and pickup his samples of shirt options. Oh, and we still need to figure out what the hell to print on 'em! Where are all the designers around here?!