Hi,
You may wish to contact Sue at FDTS seatbelts. She supplied me with two when I had the rear seatbelts made. Please note they are not exactly the same as these but will do the job.
Are you sure these are supposed to be "seatbelt hooks". perhaps they are intended as hooks for netting when folding the seats down and transporting something in the rear. They are plastic and would break away in even a minor collision.
I have a pair original seat belt hocks for the tongue of the early retractor or 3-point belts.
These are used to hang the belts in place, when not fasten.