Answer:
The library may have a copy of Gun Traders Guide, or the Blue Book of Gun Values, but it will likely be out of date. A more current means of establishing worth of everyday guns may be to check the on line gun auction sites, such as gunbroker, auctionarms, and gunsamerica. Search for the make and model of your gun, and specify CLOSED auctions. Look at the prices they actually sold for, not the high reserves with no bids.