It looks like you can order just the spare alloy wheel/tire OR the tire/wheel and jack kit! Did you try asking a dealer IF they can get either one? Or maybe try a Canadian dealer... sometimes they can order RoW parts easier than US dealers.
Spare tire and jack kit 71100445667
or just the alloy wheel and tire: 36110445045
IF those two parts are truely not available in the USA, you could always order the e60 spare tire kit (tire, wheel and jack kit). But thats a little bit more money and space.
I think my BMW dealer originally said the alloy wheel/tire was like 160 euros. But they cut that down to 120 euros for me.
I really like this wheel bc its very light and compack. I just did not want to drive to a far away land like Italy or Austria and get a flat tire and THEN be stuck there for days until I could get a replacement tire. I woud rather carry this spare tire around - JUST IN CASE. Just to get my back home to DE.
As for the flimsy jack... yea... I know. It only has to work once or twice. I have a nice German floor jack for all my service/maintanence needs.