Try
www.thevoiceofmusic.com. Most Zenith turntables from this era were built by VM and Gary can likely fix you up with a motor for a reasonable price. If not, any motor from a similar vintage VM record changer should work. And, I don't blame you for not plunking down $70 on a basic record changer. VM built changers were very common back then; and, you will find one much cheaper if you look.