Someone posted on Mini2 about getting some OEM wheel/tyre sets fairly cheap and I see the German dealer (Leebman.de) has an eBay shop selling F56 TPMS sensors for about £9 each - presumably not OEM ones, but at that price who cares?
The wheel buyer said is was £90 to ship a set of wheels, so it looks like a good source for winter wheels.

The wheel buyer said is was £90 to ship a set of wheels, so it looks like a good source for winter wheels.