Heh, besides the phone and calling, I don't the info is there anymore.
I just checked, the purchase history only goes back 18 months.
Back in the old days, heh, they did the QT Pro unlock key via email, would of been from "order_acknowledgment", any chance you have old email squirreled away somewhere?
I think I ended up buying it twice, like you, couldn't find the original email/key and bought it again in 2009, but kept that email around. It late at night, was in a rush and wasn't sure it could be recovered.
Odd about the X and 7 giving that message, I've had both installed on the machine since X came out.
Good luck but I doubt if the info is "on line" anymore, you'll have to give them a ring.