I have used the following from McMaster Carr:
Part #9506K14 for 50" length or
Part # 9784K45 for 100" length
To cut, use a good pair of scissors rather than snips.
Here are the specs:
Shim Stock Rolls
Stainless Steel Type
Type 301/302/304 Stainless Steel
Width x Length
12" x 50"
American Society for Testing and Materials (ASTM)