I've heard different views about doing after market or custom upgrades on Glock pistols. Many say it's not really needed but if you desire improved use, check out these sources:
www.Glockstore.com www.Glockbooks.com www.Customizeyourglock.com .
Lenny Magill's Glock Store offers a few trigger & spring units. Morgan Boatman's Glock websites offer insight on repairs & custom work.
Clyde