Is there a such thing as super stretchy elastic?
What are you needing it for? There used to be a clear elastic that was often used in making swimwear that was very stretchy. I've not had the need for it for some time so I don't know if it's still available or not.
I used to use that clear elastic in doll clothes,after awhile,it tends to dry out and break.Of course it lasted a couple years,and it was/is doll clothes,so this is a JFYI.
Like the op said,what do you want to use it for??