I got my copy from whatever med school it is that employed the guy who made it. I believe the school was somewhere in the midwest. As I recall, I had to call their bookstore and order it by phone. Also, I know GW uses it so they might have copies available at their bookstore as well. Sorry I can't be more helpful but maybe that will give you a start.
Edited to point out that it is in fact a great resource but the program looks like it was made in 1988. Using it takes me right back to my macplus.