Mmm, shiny ! - UPDATE
Looks like the new LEGO® Star Wars™ 10th Anniversary Stormtrooper™ Magnet set is now available to buy from LEGO Shop, at least for US & Canadian buyers. Priced at $9.99US / $14.99 Canadian
Thanks to Andreas for the info :-)
UPDATE - we've been informed that the LEGO Brand Store in Milton Keynes, UK, has received a delivery of 'Chrometrooper' magnet sets & they are already on sale. The assumption is that the other UK Brand Stores have also received them, but this is unconfirmed, so, as usual, check before starting your journey !