Ray, as far as I know no one makes that spring-loaded lift assist part these days; but the good news is there are millions of them attached to currently-existing cabinets, from which you'll have to harvest one.
If you manage to acquire one, do be careful installing it--it contains a spring that is under a tremendous amount of pressure, and if it "gets away from you" during the installation process it can be nasty. If I were in your position I'd simply find a cabinet that already had the part installed to save myself the trouble.
With any luck, you won't have any trouble finding one. Hardcore sewing machine collectors often have more cabinets than they know what to do with and are happy to unload some.