What to purchase DSS to Wave Converter developed by James M. Voelker, but his site www.turbodictation.com has expired.
It's not possible to buy the software again, because, just like you said, the official website is discontinued. Luckily, this isn't the only application available for this operation.
There is iDealShare VideoGo that has the capability of loading DSS files to convert them to various audio formats. You can check it using the following link: http://www.idealshare.net/audio-converter/convert-dss-to-mp3-wav-wma-m4a.html