No records in the public domain.
Harrington and Richardson made it.
Cornell Publications may have a book on H&R history
Harrington & Richardson did not make a Model 1900. Hopkins and Allen did.
Your harrington and richardson model 900 was made between the years 1962-1973.
2013
There is a company called Harrington and Richardson. They have made shotguns, rifles, revolvers, had military contracts for the M16 and various other weapons. They tend to be functional and basic, not high end.
10-100 USD or so
1971
No where. They went out of business several years ago.
1987
These are rather scarce, as MOST were made as .410 shotguns. Values can range from ABOUT $150-$500, depending on condition. This is NOT a cut down rifle, but was made as a handgun from the start.
"P" prefix indicates 1953