Buy on Cloud9 Web Store
IMPORTANT
If the Cloud9 product you purchased doesn't have an FSDT updated installer yet, you have to install the Cloud9 product first, then update the Stand-alone Addon Manager, otherwise the "Register Serial" option, that is needed to activate your Serial Number, will not be available.
The Stand-Alone Addon Manager is available on the links below:
FSX Version here
FS9 Version here