The vac system is normally just the motor and blower. The bag was in the hose and handle. If you stick a normal vac hose in it the switch will contact and it will run, but without filtration. I had one in our 76 Argosy. The bags for the OEM "dust bubble" are no longer made. You might be better off retrofitting a really small shop vac into the space and using it if you want the central vac features.
Of course all of this only applies if it is like the one I had
If it has a bag in the built in portion you can just get a hose and a few attachments