Much of the used furniture in the smaller cities in Uruguay seems to end up at the Remate auction houses. Many of the remates are online, so you can see what is going to be on that week's auction. I have picked up some pieces at the feria, and some thru FB Marketplace and other fb groups , as well. In Montevideo, they used to have used donated furniture, along with the new stuff that the clients make, at the Remar drug treatment shops. If you end up going into Buenos Aires, the huge Salvation Army Thrift Shop there has rooms and rooms full of furniture, as well as all the other used stuff. Shops that resale clothing in both countries usually have a sign that says FERIA AMERICANA.