Some musical insturment stores can order custom sizes of Anvil cases - or other brands much like Anvils such as Hybrid. These are the cases you see rock bands using to haul equipment - I've actually seen a bus roll over one with no damage to the contents. Years ago I had one made that's the size of a large briefcase - my 8x10 fits inside perfectly, although folded.
You can have one made to your dimensions, but be prepared- they're expensive although worth it if you need the protection. You may be able to order them on-line now.