Besides the Audiomedia 3 and some old M-Audio Audiophile there wont be a lot of a choice if you need OS 8 Support.

Sometimes those actually go away on ebay pretty cheap.

I know the M-Audio Revolution 5.1 and 7.1 have OS 9 drivers as well - never got those working tho back when I had that card in my G4. Also it might actually cost more than a used AM3 or Audiophile if youre lucky.