My brother-in-law says that one may not sell hog maws in Oregon. He contrives to get some now and then from Pennsylvania, where he and my wife grew up. Even at farmers markets in central Pennsylvania, though, one must order ahead for them.
Probably go in on a hog with some 4H group. A lot of my coworkers in smalltown/semirural areas will raise pigs. Not sure if it would be a violation to see hog maw (had to google, now I want some) but probably nobody would care.