Soundcards are getting hard to get by.
The folks at A1k.org have recently done a re-engineering of the Prelude. Also, they created the so called „amiblaster“ sound card.
You could ask DJCook from A1k, who also is on AmiBay.
Maybe he could help you.
Other than that - good luck on eBay and AmiBay and whatever sources for used hardware you might find.