Can you give a little bit more info on what your using the washer for? A shank washer is usually a rubber washer that goes in your toilet. Are you talking about a rubber high temp gasket or are you talking about a round metal washer, typically referred to as a fender washer?
Basically if the item you want is rubber, it should be high temperature and if the part you are talking about is metal it should be stainless steel. These are things that, while sometimes available, are not very plentiful at local hardware stores, especially if you are looking for lots of parts or sizes.
With a little bit more info on what your trying to do the group should be able to give you some more help.