All you have to do is send them a template and tell them what stock you want and they'll make them. Make sure you have them mirror polished or some other way of closing off the surface to possible corrosion.

Garhauer made my new chainplates for $85.00 a piece. 3/8 stainless, 16" long, 2 inches wide and a bunch of holes followed by polishing. Good piece of mind price.