You cannot buy a GSX account, you have GSX access ONLY you are a service provider (repair shop) or a self-service-account.
If your organisation is neither (and not interested to become SSA) your best chance is to make a deal with the company that repairs all your Mac's, they may be kind to you and create an account connected to their GSX account, that gives your JSS access to GSX data, but they are not supposed to do that. Note that some info (like warranty status ) is public.. maybe some API programming can read warranty status?
