TBH unless you need to keep the oars in the rowlocks I probably would stick to standard rowlocks.
If you do want to go the 'RNLI' route it may be a case of getting Rib Shop or a tube manufacturer to make them, or have a bash yourself. Basically it is a loop of webbing bonded into a hypalon patch. Not sure what the 'X' pattern you can see under the hypalon patch is (stiffeners to spread the load from the rowlock?)
Seen to be a 2inch webbing then a smaller black webbing around that running the the opposite direction. Then with a simple Hypalon patch.
Looks like you good easy make one of needed.