During the 1970's Daisy bought the rights to S&W airguns they renamed the 78G and 79G to 780 and 790. You may want to contact Daisy Airguns and ask them for a diagram.
see link below.
Try a large well stocked air gun shop.
I would do a search on the web for "Air Gun Repair," there are shops that make a living repairing air guns. Or see the link below.
Do a search on the web for "Air gun repair" and locate a shop near you to repair the air gun, or See the link below.
It's going to take some searching. I would contact several of the places that I have listed on the link below. Or do a search for "air gun parts" on the web
air soft pellets
50-500 usd
100-300 USD depending on condition
Model 37
This pistol was made between 1971 to 1980. I am unable to place an estimate of value. Because you gave no description of the pistols condition. Without more information it is not possible to answer your question
No-one seem to have a diagram on the repeater but I did find this on the web. see the link below
The serial number C642424 was assigned to the Smith and Wesson models 10,11,12,45,Air crewman and there pre model variations.The year of manufacture for your serial number is between 1963-1964.
You will have to find someone who specializes in air gun repair.