You might try John Holmes of Surplus Marine Electronics (I think he is in Poole or Bournemouth area). Tel 02380 860422 or mobile 07885 746705. I have spoken to him in the past - he seems to buy up older instruments and transducers when they are replaced/upgraded. Have never actually done business with him so cannot vouch for his reliability.
Just bought an 'unobtainable' repeater from John. No problems - he was very helpful. Seems to keep a lot of bits in France so it can take a few days to get some items.
