There are 5 Waco ZKS-7 aircraft on the U.S. registry that TailWiki has a page for. Every one is built from the public FAA record — year, serial, engine, home base, and registration history — and owners and pilots add photos, trips, and stories on top. The ones listed here were built between 1937 and 1939.
N20902
1939 Waco ZKS-7
Hollister, MO
N50662
1939 Waco ZKS-7
Lorton, VA
N17457
1937 Waco ZKS-7
Ellsinore, MO
N17701
1937 Waco ZKS-7
Horicon, WI
N17741
1937 Waco ZKS-7
Bates City, MO