Find 32-bit executables in a given path. Uses the macholib module that ships with macOS.

find32bit.py

#!/usr/bin/python

from macholib import MachO
import macholib
import os
import sys

path = sys.argv[1]

for root, dirs, files in os.walk(path):
    for file in files:
        abs_path = os.path.join(root,file)
        if os.access(abs_path, os.X_OK):
            try:
                macho = MachO.MachO(abs_path)
            except (ValueError, KeyError):
                break
            if len(macho.headers) == 1:
                if not isinstance(macho.headers[0].mach_header(), macholib.mach_o.mach_header_64):
                    print('%s' % abs_path)

I modified the script to address the issue @aschwanb (and I) were seeing.

Since you can't seem to PR a gist, here it is: https://gist.github.com/lazymutt/d6b145f14437e9eae1e7174058618b1f