single button key fob, sigma type

Both the key fobs are working well, the rear side of the cover is rubberised or softer than the front side and is starting to deteriorate so would like to put the gubbins in a new cover.

I would like to buy the new cover only, to transfer the key and internals over into, can't find one for sale anywhere, a couple of sellers on ebay offer to refurb the present key but a new casing isn't part of the deal far as i can see.

Anyone know where i can get a new empty cover from please?

There's loads of Toyota casings available because the original key fobs were made of cheese and eventually broke up (got the T shirt), Subaru/Sigma keys are strong and well made so unless they get worn by jingling around with coins etc in your pocket they last pretty well the life of the car.