I am on the email list of R&W Rope https://rwrope.com/.
They obviously sell rope but their website shows many items of marine hardware that may be applicable to Grand Banks.
In particular, R&W Rope offers many items from a British company - DAVEY & COMPANY LTD. In addition to pulls and latches that look like they belong on a GB, they offer two different sizes of rail hinges that look identical to the originals.
Take a look when you are searching for hard to find hardware.
No connection to the company.