I saw something good while looking for something else the other day...let's see...There we go:
http://www.coloradocase.com/pages/Guitar.html

They sell gig-bag like cases designed to fit over a hard case, or soft gig bag cases with fiberglass reinforcement:

http://www.coloradocase.com/pages/Fiberglass.html

Some of them can be ordered with backback straps instead of one shoulder strap (not clear if all can).

They also sell bagpipe, accordion, cello, harp, etc. cases. Looks like they custom make a lot of them so you might be able to get what you want.