Ypu might try Numrich gum parts. They have the largest inventory around..Try gunpartscorp.com. Maybe they can help.
1901 single barrel shotgun, washingtion
The Harrington Richardson 20 gauge single shot shotgun, Feb. 27 1900 is valued at $75 in poor condition. In good condition, it is valued at $200.
H&R / Harrington & Richardson
Seek the services of a good gunsmith
Under $100.
Unlikely that detailed sn data has been published.
Seldom exceeds 100 USD
Value will seldom exceed 100 USD if if great shape.
In 100% condition, $100-$125.
Since you do not say, whether your Harrington & Richardson is a pistol, rifle or shotgun and you do not show a letter prefix to the serial number, I can only give you limited information based on a Model 48 Topper Single Shot Shotgun which was manufactured for a period of 14 years between 1943 and 1956. I hope this helps, until you can supply more information on your shotgun.
serial number suggests a single barrel, hinged frame Model 1908/08 shotgun - if so - 1920-25.
Topper is a brand name of a line of basic single-shot shotguns made by Harrington & Richardson. H&R is owned by Marlin Firearms Company.