Some Chevy IIs/Novas came with a heavy duty suspension, which included a single leaf rear spring that was double the thickness of the stock unit. I found a set in a wrecking yard under a station wagon, bolted right on, great for hauling sacks of concrete.
As you well know the standard single leaf is a wet noodle. I'd check Hemmings Motor News or Nova Club etc for the best deal. Also Global West Ent. in So CAl had some kits that greatly improved the crappy front suspensions of those cars.
Best of luck!