I think that if you bought 2x10thou and 4x5thou you would be covered.
The larger Enlans, the EL series have 20 thou per side, always. I'm guessing that the tighter the tolerances the less washers you would need so a better made knife would be less than 20thou per side 2x10 and 4x5 gives you a good range, 5, 10, 15 and 20 thou per side.
I always measure the washers that come out with a digital calliper to get the size for replacements.
I also flat the blade tang and liners with wet/dry as well as the new washers, also the pivot hole and pin with Solvol Autosol or any slightly abrasive alloy cleaner, - results buttery smooth. A light oiling with your favourite lube and you're good to go.
Edit............. I forgot to mention where I bought them, if you are in the U.S.A. then the postage might but in the U.K. it costs way more than the order. Anyway
U.S.A. Knifemaker stocks the phosphor bronze washers.