It shouldn't be that hard to find a replacement fan. Heck, for my CyberstormPPC, I went to a local computer store and bought a second-hand PC fan and heatsink. I then took a dremel and modified it to fit.
Either that or try an electronics supplier. We've one locally that can usually order anything they don't have.
As far as the A1200 goes, yes, you can build one up enough to rival the 4000.. Just depends on how much you want to spend. (Both my 1200 and 4000 are similarly equipped.. Mediators, Powerflyers, PPC accelerators.)
