I'm not a case expert...but i have moded a gibson case for my fender J
Likewise i just cut the existing foam.
Most likely you would find foam with the right height and size.
cut the shape.
Finding some furry material to line it would be a quick trip to the
fabric store.
You would have to trim it nicely and then attach it with a very light spray adhesive, or brush it on by buying a can of cement.
not sure if certain glues react to foam.
Otherwise as you may know the ripper case followed the shape of the body.
Buying a case might be a good idea, because after you buy the materials like, foam, fabric and hardware. It could be over or around 80 to 120$ the same cost as a new case.
as far as locking the case if someone wants to steal it they will just pick it up, the best use for case locks for me was to lock yourself out of your own case after losing the keys, most likely 10 minutes before show time, but thats just my luck
I found this original
Ripper case
and found this new
Epiphone case
As far as the Ric case......well it looks like you get to buy a Ric too to match that case.

or sell it to a ric owner who may be interested in restoring a matching original case.
coffin case are cheap as hell, ive had 2 of them fall apart on me, so never again.