I'm not sure what you mean by "associated hardware". Are you referring to the follower?
Anyway, a magazine spring is a magazine spring. It's nothing but a coiled spring of a certain diameter and length. If you can't find one specifically for an 11-48, I'd try one made for ANY 16 gauge tubular fed gun. As I said, a spring is a spring.
Followers are about the same way. They are just caps that fit over the end of the spring to keep the spring from coming out of the tube. If you can't find one for an 11-48, try another one as long as it's the correct gauge (16 gauge). Good luck.