The GasOne stove connector would be used on a tank like this one with the large external threads on the valve, known as an ACME fitting.

I'm not sure what a "Malta" style connector is but if it's like the old POL (Prest-O-Lite) connectors with internal threads, there are adapters like this one.

The review comments on this Amazon product listing for a tank adapter seem to echo the feedback you received from Weber about the code and that this thing was all they needed: https://www.amazon.com/GrillPro-11051-Universal-Propane-Adaptor/dp/B0029T5U0A