Hi There,
As you have already been informed, these were both double ac-
tion and single action. Without being able to observe the lock
work, the most likely problem is with the rear sear (the single
action sear) and/or the notch the rear sear engages.
I have not worked on the .44 DA but I have worked on its little
brother, the .38 DA and a good smith can either build up the
damaged part or re-forge the part.
Try Jack First Gun Parts. They have a few parts for .44 DA 1st
model (they list a rear sear and you can give them a call).
Cheers!
Webb