Not sure who you can send them to, but with a small credit card diamond hone they aren't hard to diy sharpen. You sharpen them like router bits, check youtube if you are unsure.
If there are machine shops in your area you can ask where they send their milling cutters to for sharpening. Chances are there is a local place that can do the work.
There is not always a good local place. Many shops send what they do sharpen out to have done. That said, I do still sharpen pen mills, HSS or carbide. Better price if you have several at one time. Shoot me a PM if interested.