Coincidentally, I'm looking at an NT1-A shockmount bungee right now. I picked it up off the floor while moving from my old recording space into my new studio. It took me a minute to figure out what the heck it was. I think the mic had originally come with a spare.
This bungee is much stiffer than others I have. The one on my Shure shockmount has an elasticity similar to those bands you use to hold a pony tail, rather loose and floppy. By comparison the Rode's is much more taut.
With such a variation, I'm leaning toward the theory that the degree of elasticity is not calculated by rocket scientists at all and may not be all that important. My intuition says to err toward looseness, on the theory that an overly-rigid shock absorber might not be as responsive to very low frequencies - and that's the main reason these devices exist in the first place. As long as it's stiff enough to hold the mic up, I'd think it would be OK - and the NT1-A is not a particularly heavy mic.
I'd go down to the drugstore and pick up a few of those hair-holder things and see how they work. I think they're cheap, and just imagine how cool a fluorescent pink one would look.