OK, the trigger return spring is in the front of the trigger. One end is trapped between the frame and the trigger guard with a hole for that screw to go through. One of those springs can be easily made or an Iver Johnson spring from Wolff can be modified.
The part you circled, that looks something like Cinderella's slipper, is the single action sear. When the hammer is pulled part way back, it engages with the safety notch; when the hammer is back all the way, it engages with a notch you can barely see at the bottom rear of the hammer. The other piece that extends down into the grip is the spring for the SA sear. If it is missing or broken the SA sear won't work and the gun will be DA only.
The SA sear is disengaged by the trigger contacting the "toe" of the "slipper", pushng it up and tilting the rear down to disengage from the hammer.
The spring can probably be made fairly easily; the SA sear itself would be very tricky to make and probably cost more than the gun is worth.
Jim