No the shims are for spacing the washer off the bearing. It contacts the inner race of bearing only, so you don't ride the washer across the inner and outer races. This will add friction and heat the bearing up, making it fail prematurely, just like the clutch bearings will do with full size 5x10 shims. I had a thick washer in my pit box, but basically any washer with a 5mm inner diameter and say about 2-3mm thick will do. This mod is more important when running the plastic rear brace, which a lot like to do. I actually sent a email to Losi about this center rear axle being too short. My Kyosho and Mugen are plunged way into the drivecups compared to the 8ight.
You could stack up some .3mm shims up instead if you couldn't find a washer IMO.