I have completed the first batch of 922(r) compliant hammers for the M4 (though I think that also fits the M1, M2, M3). These are rolled plate tool steel, wire EDM cut, and NiB coated for smoothness. laser engraved to identify them as US made. Price is $85 with free delivery.
These are not 'exact' copies of the factory. There were two issues I saw with OEM that I addressed:
1. When cocked with my finger off the trigger, the hammer could hang up on the trigger body before the sears came fully into contact. I'll make a video, but it meant there was a click when you touched the trigger, as the hammer popped fully into position. I fixed that.
2. When dry cycling, I got the hammer to drop as it was resetting. It only happened once or twice, but I added a little meat to the sear to make the handoff more reliable.
As mentioned above, I added NiB coating, which smooths pull and might reduce pull weight slightly - though I have not measured how much.
Also, I've come up with a version that makes it into a 2-stage trigger. At this stage, pull weight is slightly higher, though this is a work in progress as I explore if there is a demand, and how custom springs can remedy it. 2-stage is typically not sought after in shotgun. I don't think it will reduce effectiveness, but it might not be a benefit, so we'll see.