I got my washers thru Grainger industrial supply for about $17 for a box of 20. They are a funky thickness just over an 1/8" each but not quite 3/16". OD is 3" and the ID is 1-3/8". They fit perfectly. They are steel.
not to hijack this thread but what is there a specific id and od for the washers? and specific material washer you need to do this?