Crusty old bikes can be found by the dozens in the basements, garages and barns of crusty old men. A friend of mine has at least a dozen, 80's and earlier, including one of those cute little Italian Harleys, all of them turning slowly to rust and aluminum oxide. Getting these folks to part with their treasures is another thing entirely. Going to vintage motorcycle events and swaps, and talking to people, showing interest and making friends is the slow but sure process that can open the door to ownership opportunities. The joke is that you make friends with the guy, then with his wife, and then you get his collection, ..... eventually.
Of course "barn finds" occasionally show up on Ebay, Craigslist, Offerup, Letgo, sometimes even at good prices. To compete in that arena, be prepared to look at each resource several times a day, and be ready to respond immediately. The best deals often last only a matter of hours. It only takes one buyer to sell out.
Gotta be careful with the pressed steel frame bikes like the one in that picture. More vulnerable to internal corrosion than a machine with a heavy wall tubular frame.