I think the old Southcoast blocks are some of the best made with the bronze frames and roller bearings…usually outlast the boat they are on. I had same issue and ended up making new cheeks from Black Locust. It’s not that difficult to do and they wear well and look great.
There are a number of articles and blogs on doing this…you may want to check out the “Wooden Boat Forum” and do a search.
I suspect they were fabricated from Buna-N rubber. Blocks of rubber
are available (McMaster.com) but shaping the rubber into block cheeks
is difficult. Once can machine rubber providing it is “frozen” in a
dry ice alcohol slush then machined before it becomes too soft.
As stated in the last post, fabricating wood cheeks is not difficult.
All one needs is a Japanese handsaw, I similar saw, a drill, wood
files and assorted grades of quality sandpaper. A band saw and drill
press speeds the job. Wood choices range from quarter sawed Douglas
fir to white oak to teak to black locust.