As far as i know there were no differences other than colour and the logo between the SPCR version and the normal silver one. Never heard anything at all about side pannel differences. My SPCR door looks closer to the orriginal door than the improved model it's definitly plastic on the inner surface, is the improved one aluminium then?
If memory serves there was a SPCR version (with a small kickback to SPCR) for a year in black, but after that then antec would just sell them in both shades at the same price.
Also it was very easy to find the SPCR model in the UK, there were at least five major retailers selling them when i got mine.