G'day unknown folk singer,
I have a recording at home (Sydney Australia) and also have Sydneys Carter's song books (~5 of them) which includes Port Mahon. If you don't get any answers (and the request appears to be 14 days old as I read it I can come to some arrangement to get a tape and/or photocopies to you. It is a beaut song and haunts me over the decades. I first heard Sydney Carter in 1972, at the 7th Australian Folk Festival.
I haven't been reading these pages lately as I have just been at the 33rd! I am about to scan in the indexes of all the books and send them to an Australian performer who recently requested info on Sydney Carter. You could presumably contact me on these threads or at my personal page.