I did a quick google search for "retinning copper". The first hit was http://rockymountainretinning.com/Retinning_Copx.htm , and there were lots after that. It looks like there are many places that do it for what seemed to me reasonable prices.
Try Oregon Re-Tinners. www.retinners.com or 800-547-7014. They are a great family ran business. Herb has been hand tinning copperware for 40 years now and does an excellent job.
Just in case anyone from Texas wants similar information:
Akers Metal Repair Richmond Ave. Houston, TX (713)527-8205
He has done great work for me. Beautiful retinning of hammered copper, repair of silver, and repair and rewiring of antique brass lamps and chandeliers.