There is a firm in Maryland that might be able to help.  It produces for
the National Park Service plaques that are custom-designed, screenprinted,
and embedded in fiberglass that are full color and withstand the elements
for quite some time.

Phone (301) 791-6920
Fax (301) 733-5379.

Address:  G.S. Images, PO Box 1288, 355 S. Potomac St., Hagerstown, MD.,
21740