I just ordered this from Royal Mail.

Celebrating Mini's 50th birthday....

http://www.royalmail.com/portal/rm/shop?catId=9300091&pageType=Others&pageId=shp_prddetails&product=prod72660035

got mine last week, very nice :)
they also do a stamp pack, think there are about 10 stamps on a sheet, they look really nice as well