al number indicates that your Parker shotgun was made between 1866-1868.This covers the serial number range of 0-6,800.
I would start my search at Numrich Gun Parts Corp.
what is it worth
10-10000 USD or more depending on specifics
We have parts for that model. firstname.lastname@example.org
I have parts for that model. email@example.com
Numrich Gun Parts Corp. online at ww.gunpartscorp.com
You can find parts for many westernfield shotguns at Numrich gun parts. WWW.e-gunparts.com