Jim68,
What may work for you in the "washer" conquest is what's called "spring washers". Those are a very thin, sort of warped washer. They are sort of bent in a slight arc. They are used when a bit of tension is needed in the connection between where ever they're used. I think they'd work flawless for you. As has been stated, McMaster Carr is a good place for things like that. Grainger and, some other specialty fastener outfits have all kinds of stuff like that.
One more thing, you also might be able to use nylon, thin washers too. They are seriously strong and, have tons of UV resistance built into them and, they also work well as sort of a self-lubing washer too. Good luck.
Scott