You can order round solid stock of different types of plastic from McMaster-Carr. If there is metal that would support both sides of the washer if the washer was wider you might make it wider to distribute the weight over more area so it does not wear as fast.
You need to find someone with a lathe to cut the material to the desired size.
Our refrigerator that was not very old wore out the plastic washer and I made a better one with my lathe and it has held up fine for a long time now. If I remember correctly I made it out of some solid bar white nylon I had. I think the nylon I used was a high density nylon and not as soft as the original washer.
When you machine or drill plastic the cutting tool should always be a new tool that was never used to machine any metal. Plastic is very soft compared to metals, but the cutting tool has to be very sharp to cut it properly, and that means a new tool that was never used on any metal.