My E17 came with some, but I don't think they'll be big enough.
There's gotta be a rubber or silicone band that will work. For example, I was looking at this one that is probably be a little too big
I'd rather have black or something that's not natural rubber band color. Obviously that one is strong enough, though. From the user comments:
"I use these bands for making traditional style, mostly tree-fork, slingshots. . . They will drive a .38 cal lead ball all the way through a steel soup can at 10 yards."