Are you reassembling a basket case? That part would be rather hard to lose if you took the bearings out yourself. It's not difficult to make one, the tricky part is the flanges that centre it "close enough" to get the axle through. Probably one of use has one from a "spare parts" bike, sorry but I do not. Some parts out of my cannibalized bikes I want to keep for spares but the axle spacer, no. They don't wear out and if one fell off while riding ... finding it would be way far down the list of things I need to do.