I have a 93 F53 chassis. I replaced the calipers and hoses about two years ago because the calipers were sticking and getting my wheels extremely hot. I am not 100% sure, but I think the copper washers came with the hoses, not the calipers. One possible thing to do is to take measurements from one of the washers on your system and purchase some new ones of the same dimensions. You can probably find ones of the correct dimension from an industrial supply company such as http://www.mcmaster.com/
Just do a search on their website for copper washers and find the right size you need. It is very easy to order from this company with a credit card. They do not have minimum quantities and will ship via UPS to your house.