Chances are that is because...#1 they haven't been made since 1960...#2 More of them were marketed under the Savage name and #3 The reciever is exactly the same as buying a COMPLETE gun..The ATF says the reciever transfers require an FFL (dealer) and the same NICS check and form 4473 as a complete gun would. FWIW, The model 775 shares the same Illustrated Parts Breakdown and parts list as the Savage Models:720-745-750-750C and the Springfield Models: 745B-745C-755-755A-775 and the 775A. BTW These models are among those licensed by Browning after they moved from Belgium to the USA(WWI moved ca 1904). When they resumed manufacture of the Browning A5 "Humpback" shotgun, they also licensed Savage and Remington(Model 11A) to make the gun.Bear in mind that the Savage and remington guns are copies and NOT clones. Meaning very few parts swap out.YOu will not find any dealer that has a supply of a dozen or so recievers in house. Mainly because these as well as internal parts will come from a parted out gun. The reason a gun is parted out(mainly) is that the reciever is crap, so the parts are salvaged.Monitor the auction sites for such a gun. You may also find some help at: www.vintagesporting.com
www.sarcoinc.com...At Sarco,you may be looking at a Mil-Surp gun. If memoery serves me here, the Savage/Stevens/Springfield version may have seen military service.