While doing my other mods, and no current run of fuzzy washers available, I kept an eye out for the 22mm ID and 36mm OD dimensions of washer.
While at the hardware store getting the PVC pipe and clamps for the airbox mod, I found a couple of boxes of M20 galvanised washers were close, but there was a great deal of variation.
I grabbed handfuls and held them in a stack looking for the right "mutation" that gave the desired thickness. I found a 2.5 and 3mm example that looked the best (construction washers, not all the prettiest examples of metal work!)
I settled on the 3mm example, just 1mm OD larger that didn't look to be a problem on the pulley recess.
If you look at M20 in these two links below, you can see the variation in the standards for what M20 should be. I can tell you in those two boxes I'd probably have found an example of all whole mm variations that I may have needed if I looked long enough.
- Table showing M20 is roughly what you want
http://www.roymech.co.uk/Useful_Tables/Screws/Din125.html
- End of page washers table showing variation in M20 standard, ranges shown you can find the perfect 3mm fuzzy washer replacement through variations in manufacturing tolerances
http://www.roymech.co.uk/Useful_Tables/Screws/Hex_Screws.htm
My example I settled on within 5min of handling/comparing was the 22mm ID, 37mm OD, 3mm thickness, is pictured here compared to the original washer (black) that it replaced.