Zenith did not offer a carburetor specifically for the 235. So you have three options:
(1) The Zenith universal carburetor that CAN BE MADE TO FIT many different applications up to 300 CID may be ordered from any Zenith dealer.
(2) By doing one's homework, one could probably determine one or more carbs that were originally used on something close to the 235, such as an I.H.C. 233 or I.H.C. 240. One could then look for a new old stock carburetor from various vendors selling new old stock carburetors, or possibly on Ebay or other auction forums.
(3) Having one of the carburetor vendors that sell new old stock carburetors do the research for you, and purchase the carb from that vendor.
In (2) or (3) above, some modification (i.e. throttle linkage, etc.) might be necessary. In (1) above the universal carb has a universal throttle arm, so physical adaptation would be easy, but calibration might not be as good, depending on the internal venturi size.
Jon.