I have cut My own out of flat stock before, that way Your only limited by the thickness of the material you buy, but You could use rod to cut Your own rings from too. Some alloys shine up better then others though, Can't remember what the name of the stuff I used was, but I really liked the way It polished up.
we just discussed this. prather used to have .050 sliver but discontinued them due to cost. we found out from dave a nlllb that if you sand and glue 2 .032 rings together you can make 1 fat ring without a line at all if done correctly. i did a few experiments and they came out perfect. .060+/-. they look great. ussing the method i did igues you could stack as many rings as youd like to make up that area