Ask some cookware shops that sell tinned copper, and look in the yellow pages under metal repair or cookware

Here is a place that gives info on copper pans and tinning, as well as a rough estimate as to how much it costs to re-tin your pan:

Here is a link that might be useful: Re-tinning Info

Check out these guys too: www.eastcoasttinning.com. In Rhode Island but close to Massachusetts.

Here is a link that might be useful: East Coast Tinning