Airsoft Atlanta have the SHS gear sets back in stock:
SHS Gear Sets are back in stock!
But, they are now better than ever with a new 9 tooth Bevel gear enhancement. Engineered with thicker steel and fatter teeth – these will not strip as easily as the previous 10 tooth gears. 13:1, 16:1, and 18:1 ratios all in stock. See new products page for selection. The new SHS gears are among the best valued sets available for airsoft gearboxes.
http://www.airsoftatlanta.com/New-Airsoft-Products-s/205.htm
