Broomvac, I have to wonder if the HEPA Cloth bags for the Perfect Commercial upright (Sanitaire clone) would fit and work? It's the same size opening as the Royal B bag, for the Royal Metal uprights, and that looks pretty much the same size opening as the Dirt Devil D bag.
Also, back years ago, a friend who had a Dirt Devil Featherlite that used the Dirt Devil D bag, wanted to use HEPA Cloth bags, and I found that the Kenmore Type O bags could be made to fit by enlarging the bag collar hole slightly.