Source for tail wheels

Last winter I had the tail skid of my Mini Nimbus replaced with a tailwheel
unit supplied by Schempp. It used a rollerblade (?) wheel with a solid
polyurethane tyre on a plastic hub with two ball-bearings.

After ten landings the hub was cracked and shedding parts and essentially
wrecked

I manged to find a replacement unit with a lightweight aluminium hub which
appears to be holding up well.

Trouble is, I found it in the trash can of a sports shop and no one could
tell me the source.

Anyone out there know where to purchase rollerblade/microscooter wheels with
metal hubs - I'd sure like to have a spare.