Welcome!
Not sure if there's somewhere to buy jigs for scrolling but from having done hand engraving I can tell you how I'd make some.
Use 2 layers of 1/8" (maybe even try 1/16"). Cut a circle just a little smaller than the coin in one layer, a circle the size of the coin in the other layer, glue the two layers up and then split the stack across the center. Put your coin in and use a couple of small clamps to hold it shut. You could go so far as to put ears on the corners so you can use a pair of bolts to clamp it shut. Just a thought.
Hmmm... I wonder if Steve has ever posted a jig. This is the page where you can search *all* of the patterns. It takes forever to load but once it does it's fun:
http://www.stevedgood.com/sswslist.htmlEnjoy!
KCSteve :->