You don't say whether you want to develop Interline agreements for the transfer of passengers, baggage and cargo or just staff travel arrangements. The mention of ZED fares implies the latter. Most airlines are not interested in the extra administration involved in bi-lateral agreements unless there is some major commercial imperative. For Interline traffic, therefore, your best option would be to participate in the IATA Multilateral Interline Traffic Agreements. It is possible to do this with IATA Associate Membership, full IATA membership will require an IOSA audit but many carriers now will only interline with airlines that have passed an IOSA audit.
If you are only interested in staff travel then write to the Staff Travel Managers at the target airlines. Many of them will be able to tell you how to participate in the ZED arrangements, these work like the IATA Multilateral with airlines concurring with each other to put the agreements into effect between them.