From my searches, that's a Royal metal upright. Well, it uses either A or B bags. You can easily tell by unzipping the outer bag and looking inside. If there's a tube leading up that you stick a bag onto, those are Type B, and they still make them.
If it's a little short tube sticking up from the bottom with a spring around it, that's for Type A. They don't make the Type A anymore (though you can still find new old stock), but it's identical to the Eureka F&G, which they do still make.
Alternatively, if you're feeling adventurous, you can get a Kirby Generation fill tube, slide it over that nub and secure it with the garter spring, and then just use Kirby bags.
