Online VAT service registration

I am trying to register for VAT services for my company on Government Gateway (as I have successfully done for CT and am in the process of doing for PAYE). The problem is that I need the date from which the company was registered - for which I need the registration certificate - but the hard copy is buried somewhere in my archives (I have been registered as a sole trader from 1985, then partnership from 1990, then company since some time in 2003), and I can't see any other way of obtaining the certificate other than registering for VAT services on Government Gateway. Catch-22! Can you please suggest a way forward?

I have found out how to do this - available through the Agent Services Account.