I would think you'd need to get it custom made from a circus company. I googled, and found this on another forum asking about German Wheels.
Anchor Circus Supply
P.O. Box 159
Anchor, IL 61720
+1 (309) 723-6435
c/o Steve Hammes
Maybe try contacting him?
These guys do cheap (sometimes free shipping (not sure about international) but I'm not sure they have the german wheel. They do have a roue cyr wheel though that is as cheep as I've seen them. Also just a class act company.
ooooh i want one!! i dunno where i'd practice this though :P