2008/2009 ?
Then it's either a windows version bought from Plimus or a Mac version from Ambrosia.
Plimus expires download links after a time or certain number of downloads, and they need to be re-activated by hand.
Didn't you just keep a backup of the installer around?
If not, send
Alec a PM or email (best is with a copy of your order information, such as name, and if you still have it, order number), and hope he sees it

*cough*
The fastest way is probably twitter ->
@infinite_ammo (if you're using it)