If it were me, I would probably reach out to a local welding shop.
I have a MIG welder, but wouldn't try myself. I'm a novice, and I wouldn't want to make a bigger mess.
If welding is a no-go, I would get a small L-bracket.everbilt-corner-braces-15304-64_1000 (resized).jpg
I'd hold it up to the area with the broken tab to confirm - if this were fastened with rivets, would the ball contact the rivet head? If it looked OK I would drill two holes that line up with the L bracket, and fasten with tubular rivets.