Judson compressors/superchargers aren't readily available. If you want one you'll have to look for one. Don't expect them to be cheap. When you find a complete NOS or rebuit one you'll have to pay big bucks. If you buy a cheaper non-complete set you'll probably have to rebuild it and look for missing parts.
The Judson is not intended for use on a 1600cc engine. There are two different types of Judsons. The 30bhp (pk ps) for 1200cc engines from ovals and beetles up to '60, and the later 34bhp for the later 1200 engines...
There are a lot of Judson superchargers being offered on eBay. If you look for Judson or "Judson supercharger" most of the times you'll find a few. You'll also find a few for sale at the second site I mentioned. Looking for Judson in the classifieds section of http://www.thesamba.com
will be succesful as well...
You can also contact Alejandro Martin. He's the Judson Guru, he sells all missing bits for all types of superchargers and he also sells complete rebuilt units. One downside; he's not cheap!!
His email: firstname.lastname@example.org
(hope it still works)
I don't know how much you know about Judsons, and you probably know all sites mentioned above, but I hope my answer is useful for you...