There is no place to acquire the software from. I've checked all the possible websites and it's only listed without any ways to download or purchase it. You can consider it as being discontinued as well.
However, why pay for something when there are other applications capable enough to replace VersionTracker Pro. For example, the Software Informer client is a free tool that packs the same features like VersionTracker Pro does, plus it offers free accounts to keep track of your installed apps.
I've using it day by day to keep my computer clean, updated and safe.