My references show the H&R 865 as a bolt action repeater, 5 shot box magazine, value about $100 in very good condition.
Have you tried a web search? Local Library? Do a web search on Harrington and Richardson Books and you will find some sources.
20-500 USD or so depending on specifics
$75-125, depending on condition.
"P" prefix indicates 1953
Harrington & Richardson did not make a Model 1900. Hopkins and Allen did.
50-100 USD
50-100 USD
About $70, depending on condition.
Harrington & Richardson used the Prefix AT in 1983.
1930's-40's.
Your harrington and richardson model 900 was made between the years 1962-1973.
I purchased a new Harrington & Richardson 12 gauge model 088 from K-Mart in 1980.