NM grip frame adaption to use on an old model.
Option 1. Just cut the spring shelf off of a NM trigger and have it tig welded or brazed to your OM trigger.
Option 2. No one sells the adapter, it's too easy to make one for anyone to buy one. Below is my style that I've made for my grip swaps. The hole locations are the only important features and they don't have to be exact. Just copy the size and location of the return spring hole in your old grip frame, and the location of the retaining pin hole from your new grip frame. The contour of the top is based on clearing the bottom of the hammer when cocked. I use aluminum because it's easiest to drill and shape.
Use the old model Super BH wide trigger to fill the wide trigger slot in the NM grip frame.
Option 3. The very simplest. You can use a fired .22 LR case to hold the return spring and plunger in place. Again use the NM trigger return spring retaining pin closest to the trigger shown below to hold your OM trigger return spring/plunger adapter or .22 case in place. File a small notch in the .22 case head to nest on the retaining pin.