The Book of Exalted Deeds has them:
Exotic Ranged Weapon
Cost: 1gp
Weight: 3lbs.
Range Increment: 10ft.
Max Range: 30ft.
With a ranged touch attack, instead of dealing damage you can entangle a creature's arms making them "partially entangled" - causing a -2 penalty to attack rolls and a -4 penalty to effective Dexterity. The target's speed is not reduced, and it can still charge and run but if are holding onto the other end and succeed on an opposed Str check, they can only go as far as the rope allows. Casting a spell while lassoed requires a DC 15 Concentration check.
Getting out of the Lasso can be done with a Escape Artist check DC 20, bursting it with a DC 23 Str check, or just damaging it (it has 2 hp). These are all full-round actions.
Or, if you wish, you can just use the lasso to make trip attacks - and you can drop the lasso on a failed attempt to avoid being tripped yourself.
J from Three Haligonians