You might find what you need at webdept@gunpartscorp.com .
Generally, you can't. It might be possible with Browning, but, you will need to call them with the serial number.
Remington
If you can find one, yes.
You find a gunsmith.
== ==
None published. Try shotgun collectors.
NUMRICH.com
Under trigger
Not enough information.
Look up the Marlin shotgun with the same model number.
It is difficult to find even 10 gauge shotgun ammo today. I have my doubts if 8 gauge shotgun ammo is even made any more, but corrections welcomed.