JW - there are plenty of both available, one simply has to look. Sometimes instant gratification is not an option, one needs a wee bit of patience.
As to the Chinese knock-offs: if one has thousands of dollars of test equipment, and more thousands of dollars in spare parts, a lifetime of experience DESIGNING and repairing carburetors, and figures their time is worth absolutely NOTHING, then the Chinese knock-offs are cheap!

I linked Lars' post, as, along with Cliff Ruggles, they are the two most knowledgeble men of whom I am aware with Rochester Q-Jets.
Guessing someone that specializes in Zeniths could find about the same issues with the knock-offs.
But to each their own.
Jon