@danr there is some basic research being done on the regrowth of those hair cells.... see
https://www.hearingreview.com/hearing-products/accessories/components/study-shows-hair-cell-regrowth-new-drug
This certainly is not a short time solution.. but you should know that there are thousands who, like you and I, have this problem ... Loud Big gun noise did a number on my left ear when I was 19... I am now 83... Cochlear Implants were recommended when I was 43... but they were experimental in those days.. and I made do.. and got by... now You have a much more sophisticated Science on your side.. Ken