The only guitar amp shop I know of that sells them, the little transistors for vox organs, is getting $10 apiece. I'd take a DVM over to this junk shop, check a couple, and make an offer. Ebay shop could be in your future.Just a few km's around the corner from my place, there is this 'junk-shop' with heaps of overstock from nowhere, and in a dark corner in the deepest cave of this partslabyrinth is a 'wall' with endless little trays in it. OA... diodes, AA..., AC... & AD... transistors. Hundreds of them.
..."(a) good audio preamplifier." Not a pleasant distortion generator...
With 0.2v instead of 0.7v , the crossover distortion in low power amplifiers the germanium is much better. 2SB324/2SD352 were the best for portables .From a listening point of view, germanium might be better than silicon. At the moment I am listening to an all germanium portable radio that was popular in the '60's. Sounds great, better than any silicon equivalent.
Would have to suggest that if you want a "good" quality pre you use modern good quality parts. Old germanium diodes and transistors worked for the time, much better are available now.