Andy,
My mast gate was just like Peter's and I should think you could get a new one from Z Spars if you ask them - they are quite helpful with requests for old spare parts.
However, I agree with Peter's observation that it does have a habit of catching the sliders as they go past and it is made of quite thin (bendy) metal. I had a very slightly modified copy made in stainless steel by a local fabricator which was a lot stronger and designed so it didn't catch the sliders so easily which was much better.
Unfortunately I can't find it at present (I use a totally different system now) but if I do manage to dig it out I will send you a photo.
Jonathan
P325 No 23 Tilikum