There's a slingschot forum i belonged to for a couple of years ( i cant find it right now) and although is shoot a wristrocket myself, the best shooters an builders al used surgical rubber in SHEETS!
12" x 12" wich they cut up in tapered strips 1" on one side, down to 1/2" on the other. To produce somthing like 10 strips per sheet. They swear that these shoot harder and straighter than surgical tubes... They also give you some artisitc freedom to make your own fork, since the ends don't have to be as narrow as to hold the regular tubing...
Here in Holland it's pretty damn hard to obtain some 3/8 steel shot. i just can't seem to find a factory that makes bearings. And these steel ball aren't sold in stores as amo, since slingschot are illegal weapons where i come from...

P.S.
For that reason i use marbles as shot...
