Borrowing from our "friends" who shoot shotguns ... also used for slingshots, and can be (carefully) used for blowguns.
Since the ball ammo here is NOT designed for blowguns, be careful that the ball OD passes through the barrel. There is really not a lot of quality control for their original pirpose is NOT for blowgun use. I suggest manually testing each and every piece before shooting. Nothing like popping an eardrum trying to shoot a marble, and having it get stuck half way down the barrel.
I found a great source for target marble ammo, 5.400 (approx) 11 mm (7/16") 30 lb. $45 Free shipping.
100 3/8" (9.25 mm) Chromed steel balls $10.37
How about alternative ammo (OK, thinking a little "Dennis the Menace" here ... )
Some for hunting, plinking, etc.
Muzzleloading Roundballs: <a>https://www.ballisti...s/products/704/</a>
Shot & Slugs: http://www.ballistic...departments/63/
For hunting - calls:
Finally found a source for flechettes -
1" flechette $10 / lb http://www.rvow.com/.../index.php/misc
These would be substituted (carefully) for the CS "Shotgun" darts. A lot heavier.
There are also practice tranq darts avaialable. Super heavy 0.50 cal. Real tranq darts require a license (vet, animal control, etc. - sorry! )