I could be mistaken, but I think this might be something that bc_chris does. I believe he works for some sort of clothing embroidery/silk screen place.
Corporately, I've used Garment Express before and they did a reasonable job. Our t-shirts weren't a complicated design and two colours on a white shirt so not hard to screw up. They were able to get an order of 100 to us in a week.
http://garmentexpress.ca/index.html
Have also used Genumark, although they were much pricier. We also had one screw up with an embroidered product, however they were quick to fix it and compensate for the loss, so while it was an inconvenience, it was handled well.
http://www.genumark.com/