Hi Rob
I had my original Whirlaway from Malcleanse. When the castors packed in after a few months he replaced them for me with "some better ones".
These have worked without fault for about six years, though I don't use it all that much nowadays. I grease them every so often but certainly not after every use.
Malcolm tends to source a lot from Dual Pumps but prices from Malcolm tend to be OK so drop him a line. Be sure to stress that you do not want the standard OE ones.
Mention that he got the replacements for my in 2008 (ish). I'm sure he will have this detail to hand