I am looking for an H&R model 1900 Small frame Locking bolt.
I have checked with Numrich and they only show a large frame in stock.
I am in process of repairing a .410 Shotgun and the locking bolt is separated in the center of the two halves of the strut portion. It has been repaired once prior with Brazing that has failed. I will attach photos shortly.

If you can't find a new part, maybe a good gunsmith can weld (not braise) it back together?

That is an option I have thought about, however I would like to at least try and locate one before I go that route.

You might try Jack First, Inc. The one they have on their website looks a bit different, but they are worth a call and can tell you.

https://jackfirstinc.com/product/hr-locking-bolt-assembly-730-048-309/

cool place, thanks for posting

Not sure where you are but Lee's Gun Parts in Irving has a truck load of parts.
http://www.leesgunparts.com/

Thank you all for the recommendations, I have already been to Lees, the two he had were as bad as mine, just damaged differently. Jack First doesn't have the part for this model. My Gunsmith is checking on doing a 3d scan, making a 3d print to fine tune dimensions and send updated CAD file to a waterjet or CNC company in Garland is where I think he said.

These are just a couple of results that popped up doing a quick search on Ebay. A lot of people post parts for firearms on Ebay. Easiest place to track down something unusual or out of production. Good Luck.

EBay Listing #1

Ebay Listing #2

The 20 gauge is a large size receiver and the locking bolts are different sizes, and the cam portion at the rear is rounded, not squared. Thanks for looking!