Just finished tracking down some gooseneck parts for my 84 E-35 with a Kenyon mast and boom. If you have Kenyon which I'm sure you do try http://www.rigrite.com/index.htm
You will need to get the boom cross section measurements so you can be sure which section you have but after that it appears pretty simple.
If you are located in central Florida there is always Don's Marine Salvage in Clearwater. I hear he has just about everything. Will check him out this fall.