Here's how to make your own solder washers to retain plastic wheels on .047 wire:

Use a piece of thin sheet tin (K&S #254 Easy Solder Tin Sheet, or tab material for batteries) and with a brad, hammer a small hole in the tin. Gradually enlarge the hole until you have a forced fit or tight fit on the .047 wire. With a 1/8 paper hole punch, punch out the hole. You now have a 1/8 washer that fits tight on the axle. Solder one washer on the inner axle next to the bend in the landing gear. Install the wheel and press a piece of paper over the wheel so that the axle protrudes, and solder the outer washer to the axle and tear out the paper spacer. Use a 25-30 watt soldering iron so that you don't overheat the plastic wheel.

It works for me.

If you have qualms about soldering the outer washer, then you might use a pair of dikes and nick the axle just outside the outer washer and epoxy the washer to the axle.