when i got mine Corksport was the only place, expect to wait a month or 2, they don't keep them in stock (unless youre really lucky) as they come straight from Japan.
Cusco also makes rear camber plates, but i think they may be discontinued. I saw a set of ebay a few months ago.
I opted not to get anything for the rear, as in stock form i can get 1.5deg negative, which is enough for me.
Other plates can be trimmed down to fit as long as the top nut is the matching thread.
I know a buddy of mine has some Ground Control plates modified to fit the rear of his EGT, but he pulled them out of a pile of 50, so he has no idea what car they came from.