I do not take any credit for making the ORIGINAL taser gun which is found here: http://www.garrysmod.org/downloads/?a=view&id=123389
This swep is a modified version of the LETHAL version of the Taser Dart SWEP found here: http://www.facepunch.com/threads/1109353-Taser-Dart-SWEP
Taser SWEP Non-Lethal
A taser great for RPing or having fun with friends. Shoot the taser, bring the opponent down and right click to give him a jolt. After around 5 seconds he is back on his feet and able to run away with a distortion effect. You can no longer tase people far distances. This weapon fires a bullet that will tase on hit, and does NO damage at all. You may tase as many people as you want. The only ‘drawback’ of this weapon, is when someone else tases a player that you didn’t tase, you can still “shock” his body/ragdoll.
FatBlueSloph was going to make a non-lethal version of this gun but I assume never got around to it or i’ve not saw it around on the forums. However, here’s the link to the SWEP, Have fun with it, I use it too on my server.