The replacement band for your slingshot is the 7/16 Standard Bandset.
All SimpleShot slingshots come with 2 bandsets* that may be found here: https://simple-shot.com/products/standard-flat-bands
This is the perfect bandset for MOST uses. It hurls heavy steel with great speed, yet can be tuned light to shoot 3/8 steel and even clay (tune it VERY light). Therefore, it is the bandset that comes standard with our slingshots.
* The Flippin Pickle is the exception. It comes with no bands.