All of the above, but a lot are created in easel, I buy some of Etsy and find images on Google images. I have only done one or two from the Facebook groups.
There are a few Facebook pages with free files on them as well.
the CNC file sharing group
wooden flag makers for inspiration
x carve & CNC owners
cnc for beginners
ON Etsy, Patriot Designs, Marshal CNC and Bad Dog Metal works are good files. You will find ALOT of the Etsy files are pretty rough to carve, so you can spend time cleaning them up in Easel or just use them as a template and start over.
There is a converter I use to make SVG as well it is called Cad Converter by Convertio.
Worldvectorlogo has a lot of files you just need to clean them up they tend to have a ton of layers in them that want to mess things up. So you kinda have to muddle through the file after it is imported to get it to run right.