Hi, Welcome to ribnet!
Need a bit more info here..... is it a single or a three ram device? I can't believe it's NLA on a 1996 engine - I just orderd a set of head gaskets for an '82(ish) machine....... What's the serial number of the engine? www.ishopmarine.com
has a huge selection of Microfiche, if you can find it there you may have better luck looking for the part number rather than quoting the engine number?
As a start I'd try phoning another dealer, If you get really stuck there's a place in Glasgow who haven't failed me yet for parts and will post stuff out. Failing that, the PT fluid is basically just automatic transmission fluid, so any auto factors should be able to sell you a sheet of suitable gasket to cut your own.
In the meantime, find your optimal trim setting & move the tilt pins up so both engines are at the same angle - then at least you can keep motoring.