[NightKnight]

This site sells really good bands and tubes that can be used for slingshots.

http://www.thera-band.com/

Tubes
Tan .062 ID x .031 wall
Yellow .200 ID x .045 wall
Red .200 ID x .057 wall
Green .200 ID x .069 wall
Blue .200 ID x .085 wall
Black .200 ID x .098 wall
Silver .200 ID x .125 wall

Bands
Tan/Extra Thin
Yellow/Thin
Red/Medium
Green/Heavy
Blue/Extra Heavy
Black/Spcl Heavy
Silver /Spr Heavy
Gold/Max