I don't know if you can purchase the genuine 20" cast wheel assembly on it's own, but it might be worth sending an email to sales@goldenmotor.com to find out for sure.
Please note that
standard 20" tyres do not fit the 20" MPIII alloy rim correctly and the side of the rim is not really ideal for "V" brakes either:
The alternative would be to buy a standard 20" rim that should fit, like this 36 hole Alex-DM24 alloy rim:
Although you might have a problem trying to source 48mm long spokes to lace that rim to a Magic Pie III hub:
The above screenshot was captured from
ebikes.ca.
I suggest you make sure that you can get 13 gauge spokes in that length
(ideally with 14 gauge nipples) before you purchase the rim.
Try
tillercycles.co.uk if you can't find anywhere locally
I think you might also need to file the holes in the rim slightly to allow for the 19.9 degree spoke angle where they exit the rim, as spoke nipples will usually only accommodate up to 12 degrees:
Alan
