The locking pawl appears to be riveted. Rivets can be sourced though Hanson or other suppliers.
http://www.hansonrivet.com/
If your not a stickler for authenticity, you could drill the rivet head & punch it out then replace it with a screw and locking nut after the spring function is repaired. You would need to get a good fit to insure the locking pawl functions as it should.