This may not help you with your immediate need, but I save all the shells, in bags in the freezer, from the shrimp I use for other dishes. When I've accumulated quite a few, I put them in a pan with some chopped onion, a little celery (with leaves), a bit of chopped carrot and just a touch of salt and freshly ground black pepper and cover with water. I simmer everything for, oh maybe, about 45 minutes. Then I strain it and have some pretty good shrimp stock to use when a recipe calls for a fish stock. If I don't use the stock right away, it gets frozen in 1-cup quantities.
"As a girl I had zero interest in the stove." - Julia Child
This is real inspiration. Look what Julia became!