You could try RoyalApparel. I think you'd have to buy large quantities to get them tagless (or have them relabel them with your own label).
You could do it an easier way by finding any urban wear blank shirt that you like (wholesale) and have your screen printer or seamstress relabel the t-shirts for you. Many people have other brands relabeled since not many brands sell tagless t-shirts (since they have to have tags in them by law).
A forum community dedicated to T-shirt merchants, professionals and enthusiasts. Come join the discussion about graphics, commerce, dyes, prints, collections, guides, displays, styles, scales, equipment, accessories, reviews, classifieds, and more!