I recently purchased a really decent, less-than-moderately-worn case off eBay for my earlier acquisition of a nice Retina IIIc. It even had the rare Light Mask accessory stored in its little retention area in the top of the case. (The seller may or may not have known about it. Who knows.)
If your cases are in really poor condition, no amount of repair will be less than the cost of simply finding a better one. I suggest keeping your eyes open for an eBay offering, as one possibility. It may take a while.
I have seen a few cases there for various Retina RF cameras where the cases varied from worn out junk to some very nicely preserved items.
The case I obtained through eBay was $18 with a few dollars more for shipping.
The camera retention screw did not have any method of being retained to the case, BUT a 'C' clip I had fit the shaft of the screw wonderfully. So now there is no way the screw can get separated from the case and potentially lost.
"My film died of exposure!"