One of my favorite non-silver items to stamp are copper washers, available for a great price in a box of assorted sizes from harborfreight.com (item# 93324, 110 pc. About $10 or less).
They make great links, charms and pendants and if you mess them up with too much texture there's no waste!
Michaels Craft store has some copper brass and silver color blanks some already in shapes to stamp or put in the cup and curve it. I have been happy with it. I have even soldered the silver color and the copper. They also carry blanks, and with a jeweler's saw, that costs about 6 bucks and a few blades (inexpensive too) if you are in business for some one-of-a-kind shapes.