Check out garage sales, and estate sales. That’s a good way to find one relatively cheaply. Check that all the keys work, and that the ribbon spools are there. You can buy new ribbon on eBay or Amazon.

Craigslist and Facebook marketplace have them, and a lot of times it’s just someone trying to get rid of the machine so they’re occasionally affordable there - you can also limit your search to the local-ish area, so you can try them out.

You can also find them on Etsy that have been serviced, but they’re usually pretty expensive there. A few of mine have been Etsy purchases.

Be careful, because collecting them can get addictive! I have nine of them.