Have you tried eBay.de? They sometimes come up on there, but are pretty rare. I have seen people using 19" with alternative offsets, which are close enough, if that's an option? Otherwise it's a wait and see moment.
Seems pretty common with the rears TBH. Love the alloys, but I am constantly checking mine for damage.
There is one here, but you'll have to arrange your own courier: http://www.ebay.de/itm/360959126871