Numrich Arms has parts for the 311
there is the Stevens side by side shotgun model 311
it is a Stevens, parts are interchangeable...
Have you tried e-gunparts.com?
Buy parts for 410 Stevens model 67 pump shot gun.
I don't find the Westernfield 530A but be careful: there is a Stevens 530 (1912 to 1918) that is a pump shotgun as well as the Stevens mod 530 (1935 to 1952) double barrel.
I have parts for that model. firstname.lastname@example.org
Check on Numrich gun parts corp website.
Start your search at Numrich gun parts corp.They can be found on the web.