If you will be printing your own labels, you don't want to buy "tagless" tees. A tagless tee will already have the label printed on, and it would be difficult to print over that label.
You want to either buy regular tagged shirts and remove the tag. Or, even easier, buy removable tag shirts. Several companies make these including
Alstyle Apparel - one of the largest manufacturers of blank t-shirts, Anvil, etc.
List of wholesale t-shirt brands with tear away labels for easy relabeling - tagless
Do a search here on wholesalers. They will all carry what you need, including polos. If you don't have your reseller license yet, you can also try this post
No Licensing Needed Wholesale T-Shirt Suppliers?
Tagless t-shirts 
