There's a lady in British Columbia that makes them... I bought mine a few years ago, sized to fit the 31" tires I'd just put on 'the Expensive Mistress'... not cheap (I think mine was almost $200, but impeccable materials and fit and finish), almost like a white leather jacket for your spare tire.
Take a look in the online 'my garage' photos of my rig - there's one with a slightly wrinkly brand new tire cover for it. Its now tightened up and looks awesome.
Ill see if I can find the ladies contact info tonight when I get off work - hopefully she's still making them.