Get in touch with HP Hydraulics at Fareham. They do a lot of marine stuff and have a large fabrication team - I had a pair of Arneston drives overhauled by them earlier this year. They did a great job of fabricating some new parts - considerably cheaper than new off the shelf.
Speak to Matt at All Things Metal, Shelvin, between Dover and Canterbury. Just past Lydden Circuit as you head toward Canterbury from Dover. 01303 844713. Tell him Stuart from High Pressure Services put you in touch.