I know Warp9 sells cush drive wheels for supermoto but it doesn't appear they list them on their web site. I don't see why they couldn't lace one of those hubs to an 18" rear. I'd recommend one of their Elite rims unless you really want a special color.
I've ordered custom Warp9 wheels from Toxic Moto Racing before (messaged them on FB), can't say if they'd be able to ship to you or not though. On his web site, it's an option listed during checkout.
