We've updated the Constituent (Get List) endpoint to include a new, optional postal_code parameter which provides the ability to filter constituents by postal code based on their preferred address. The parameter value supports multiple postal codes separated by commas. Postal codes will match on a constituent if the preferred address postal code begins with one of the specified filter postal codes. For example, given the query postal_code=99577,10001, the response could contain constituents whose preferred address has a postal code of 99577-0727 or 10001.

We're looking into this request. It'd likely be an enhancement to the recently added Constituent (Get list) endpoint, as an optional filter parameter.