You might try a wedding invitation shop - where they often foil stamp napkins, etc. Or call a local printer - who may use the services of a foil stamper and would be able to direct you to their source.
Thanks for the ideas. I had called a few printers and stamping on letterheads, cards, etc., was not a problem but matboard is a whole other story. Hadn't thought of wedding invitation printer so that'll be the next call. Thanks again.