how to find old looms for sale

We have a weaving shop at our museum. We have many, many looms, the oldest dating to 1740. We see looms all the time on Facebook Marketplace. Many are inexpensive, and ready to go.

---Also, you might want to contact local historical societies. (At least around here) we get offered a heck of a lot of stuff, that many museums don't have room for. Tell the museums you are interested in acquiring any looms they may not need. ~~Same goes for horse drawn farm equipment and tools of all sorts.

There are a lot of local guilds around (some of them on the internet) worth joining.  There tend to have rental looms and often there are a few starter looms kicking about.  These are usually free on the condition you pass it on to the next new weaver when you are ready to upgrade.