Sound boards are very difficult to design. There's a lot of signal processing involved, and some of the original audio processing chips are difficult/impossible to obtain, so alternatives need to be explored or reverse engineered.
S&T boards occasionally pop up on ebay, but they don't go cheap, and then on top of that, they will likely need to be repaired. Put all that together, and it would probably add up to being close to the price of the reproduction board anyway.