"former owner informed me the trigger had been worked and was light"
You will probably have to replace the trigger (which, IIRC, is also the sear) and probably the firing pin and trigger spring. Try www.gunpartscorp.com
for the parts. In the meantime, the gun is dangerous and should not be fired.
Lesson: "The trigger has been worked" is a warning to run, do not walk, away from a gun deal.