Does anyone know where I can find a 3# trigger for a Glock 21?
To get it down to 3lbs you'll need to polish a 3.5lbs connector, polished striker, and a lightened trigger and firing pin spring. That'll get you close to 3lbs.
If you want the best possible trigger send it off to Charlie Vanec. He does the best trigger job for the Glock at the moment. He uses all stock parts, but does some serious magic reshaping, polishing, and mutating springs. completely reliable, and 1.25lbs trigger. It will light any primer including small rifle. He can get the trigger weight up to 3lbs by using a stiffer trigger spring.
CGR and Tom Novac also do trigger jobs, but you have to use federal primers to get it to light reliably. They use skeltonized strikers, light springs, and set screwes in the connector. There triggers are in the 2-3lbs range.
Charies trigger is super light, super smooth, and breaks real nice. It feels nothing like a glock trigger, as close as you can get to a 1911. Everyone who pulls it, their first word is "WoW".
My IPSC buddy has triggers from all 3 (charlie, Tom, and CGR) Charies's is best. At the local GSSF event he let the Glock armorer try the various triggers. He agreed the Vanec trigger is the best trigger he's ever pulled. Heck it's what I spent my money on.
Yes it sounds like I'm on charlie Vanec nuts, but his trigger really is that good. Check out the competition forum on Glocktalk and the brian enos glock forum. There are a lot of people raving about this trigger.