You may be better off just getting new ones. They’re likely so thin (and will then be thinner after machining) that they won’t hold up. Have you measured them to see if they are thick enough as is? The minimum thickness is probably stamped into the side.
Not all mechanics turn their own rotors so you should call around. The prices won’t vary a whole lot and I would opt for an independent shop. You can also check with auto parts stores - the last time I had rotors turned it was at a Fisher’s auto parts store. I wouldn’t count on the big corporates for this (e.g. Autozone) even if they do them. But smaller, independently owned parts stores are often decent machine shops.