I have two short bits of original Koussevitzky on bass, on a compilation CD called "King of Bass II"
He plays the largo from Eccles and his own Chanson Triste. Taken from a 1920s orginal, these are quite scratchy, but otherwise gorgeous to listen to. Of course these are both technically rather un-demanding pieces, but regardless, one gets the impression that Koussevetzky was not a player who stressed in-your-face virtuosity; rather, these are first and foremost intensely musical, passionate readings.
This CD also features Richard Davis, Francios Rabbath, Stefano Sciascia, and a interesting mix of other bassists. It is released by King Records of Japan, and they have a pretty interesting bass catalogue which goes well beyond this compilation. You can check out their bass stuff at
http://www.kingrecords.co.jp/saisin/bass/index.html
Most of this will be undecipherable if your PC isn't setup to do Japanese fonts, and you'll need to read Japanese as well.
Catalogue number for King of Bass II is KICC 322, but I couldn't find it on Amazon. Maybe some helpful CD importer can find a way to get a copy if you're really keen.
Thinking about this, I'd be interested to gather other "vintage" classical bass recordings. anybody else ever come across anything ? we could start a little list here.