Support your hobbyist breeders and buy goslings/geese from them. I've seen several people in the PNW who raise them (seen them in sale areas at shows, etc). I think often the hatcheries charge a premium for the more exotic fare beyond the basic chickens, pekins, and embdens and you might get a better deal from a breeder.
I would prefer to get them from a private breeder anyway that way I can ask for pics of the breeder stock to make sure I'm not getting mixed birds, plus they can pinion birds were I don't know if strombergs goslings are.