I just wanted to post to maybe help with your expectations on this item you are looking for. The odds of tracking that item down is very low. Most likely if you ever could find one it could take years of diligent looking (just trying to say there is little hope of finding one fast is all).
You probably know this but I wanted to say it just in case
That being said there are a couple forums out there that have members who deal more in alpha/beta/preview discs (off the top of my head I know of "assemblergames" forum, but there are a few more out there if you search google for "video game collecting forum").
Good luck! Also be sure to have a worldwide search on eBay going for "Soul Reaver Alpha" and refresh/check it daily.