Is there a place I can buy replacement rubber that has an adhesive on one side? I know j hooks aren't super expensive. But I feel there's no need to buy new ones if I can just replace the rubber that has worn.
It would probably be easier and cheaper to buy some rubber, cut it to the correct shape, and glue it on. Based on personal experience, I would recommend gel Gorilla glue.
Cut the rubber, attach it with glue, place a loaded barbell on the J-hooks to force good contact.