This is the best I can do. (see the link below)
I suggest you try this web page. BTW Crosman owns both Benjamin and Sheridan air gun products. You can also contact Crosman and ask for help.https://support.crosman.com/hc/en-us/sections/200649600-Benjamin-and-Sheridan-Air-Pistols
At one time Sheridan, Benjamin and Crosman were all separate companies. In the 1970's. Benjamin bought out Sheridan and took over the company. In the 1990's Crosman bought out Benjamin. Now Crosman owns all 3 companies. When Benjamin bought out Sheridan they decided to keep the C series design. So they decided to keep the Sheridan name on the .20 mm air rifle and put the Benjamin name on the .177 and .22 caliber 392 series air rifle that looks just like a Sheridan C Series. So All Sheridan C series are .20 caliber and the .177 and .22 are Benjamin's. Crosman decided that this worked well and kept the same arrangement for both models. If you go to the Crosman home page you will find (At the bottom of the page) a link to (Owners and Parts Manuals) there you will find the owners manual in the Benjamin / Sheridan section.
Crosman co owns Benjamin and Sheridan. They supply parts for current and some older model Benjamin air rifles or they offer a service to locate someone who repairs older Benjamin rifles. See the link below. When it opens click on "Find a service center."
Start looking with these people. See the link Below.
Crosman Owns Sheridan Airguns along with Benjamin airguns. They offer a service to locate repair shops that repair older Crosman, Sheridan and Benjamin air guns. See the link below
Crosman offers a free service to locate shops that repair Crosman, Benjamin and Sheridan older air guns. Crosman owns all three air gun companies. See the link below. See the link below for all the Benjamin manuals. I don't believe the 312 manual is still available.
today. Crosman corp owns both Sheridan and Benjamin air guns / rifles. See the links below.
The 132 is part of a series made by Benjamin it covered models 130, 132 and 137. they were made in both .177, .22 caliber pellets and BB. They were made between 1946-85. The name Benjamin Franklin was a marketing Gimmick, he had nothing to do with the company. Walter Benjamin started the company back in 1899. Today Crosman air guns owns the Benjamin & Sheridan company. Crosman offers a free service to locate repair shops that repair older Benjamin / Sheridan and Crosman air guns. see the link below
Today Crosman air gun company owns both the Benjamin and Sheridan line of air guns. The .22 caliber model 342 was made between 1969 -1992. Crosman offers a free service to locate repair shops that repair older Benjamin, Sheridan and Crosman air guns and rifles. These shops usually have all the parts needed to repair the air guns. The link is on the Crosman home page. See the link below.
Crosman still has the parts manual for all it's rifles. On the home page click on "Download a Manual." Crosman owns Benjamin. see the link below
Today Crosman owns both Benjamin and Sheridan. I would contact them directly and ask for one. See the link below.