BearingCups3mmSize

Experimental product. Let me try first (see photos, not fitted to any wagons yet). Meant to fit wagon chassis kits as used for modelling in the scale of 3mm:1ft, e.g Parkside Dundas 9' and 12' wb kits.
About £10 for 36 of them in the smoothest fine detail plastic won't break the bank, even if you lose a few breaking them off the base. Brass ones will be better of course but if you can't get those, these should at least allow you to finish a few wagons and run them until you can restock. When the time comes you may have to drill them out as the rims may not be strong enough to prise them. Of course if you can get the axlebox covers off the wagon then you could drift them out from the front and re-use them another day, if they're not noticeably worn.
The design is based on some brass ones I was given for Parkside-derived kit chassis, modified only a tiny bit on the hat brim to add 0.1mm more thickness in the middle. Once you have cleaned them and got a few off the base to use, I suggest filing the pointy end flat, and possibly filing that 0.1mm ridge on the brim to make it flat, if you really think you need to. You _may_ need to clean out the insides bit more with tiny drill bits of varying sizes, but I suggest leaving that until you are test-fitting wheels. 
UPDATE - Offered for sale and no need to change - unless it's to include more in a set, as I've used a fair few already. The Parkside kits need the lead holes for the axleboxes cleaned out to 1.5mm diameter all the way through, and then from the back to a diameter of 2mm to a depth of say just 0.5mm, just the same as to fit the brass bearings these are based on. Surprisingly the rims do seem to survive gently easing the bearings back out with first the edge of a scalpel to start, and then fine point tweezers (the same ones you hold them down with to file the ends clean) but this surely depends on the tightness of the fit, and if you've managed to wick plastic weld around the outside when putting the axleboxes and leaf springs on the 9'WB kit!