You should have m2ee-tools installed on your server already, and it is capable of automatically downloading the runtime when you unpack a new deployment package. If for some reason you still need the runtime files, that are at:

http://cdn.mendix.com/runtime/mendix-7.22.0.44027.tar.gz

That naming pattern follows for each new version of the platform, with the last 5 numbers representing the build number.