I usually order from American Allergy -- we've got a 14 year old Devilbiss Pulmo-aid we use as a back up or at the outlaws, a pari proneb we use on trips and a regular pulmoaid we got a year or so ago. They seem to have parts for older models. Only thing is they don't have free shipping, so when I place an order, I usually include some bubbles fish masks and some nebulizers, to make it worth ordering.
And as far as reusing -- most of the filters are made of some sort of cotton or felt material -- they get pretty gummed up after several months usage. Especially if using tobi -- they get kinda sticky.