They're hard to find, but I've finally tracked down a place in Australia (mechkb.com) that will internationally ship me one of these convertible Cherry MX key babies, that supports both Mac and Windows, both bluetooth (pairing with four devices) and USB (for low latency gaming and charging):
Filco Majestouch Convertible 2 review: the quest for a Mac-compatible, wireless, mechanical keyboard: http://johnscullen.com/filco-review/