Finding any CD changer will be a challenge. So many radios don't even come with a single CD any more, as we're all supposed to use a memory stick with mp3 files. Personally, I don't see why I should accept lost quality from compressed files, but finding an aftermarket radio that will read uncompressed WMA files is difficult too. Although a lot of OE fitments do.
If the original CD changer is the 5-disc Blaupunkt unit, talk to these guys:
http://www.mapleaudio.co.uk/
They repaired mine a while ago. The Blaupunkt unit does wear out, and these guys know which bits to replace.