If you have an online "Free Cycle" in your area you can put out a notice for one and might luck out. Otherwise I would try eBay or family, friends and neighbors.
Thrift store, maybe.
AThat exact plate is at kohls for $30, although in person you can tell it's not well made. Target also has one similar for $20 that is better quality in my opinion.
check out a local restaurant supply house. There should be many in your part of the world. If not, then an online supply house. they will be simple, but also less expensive.
I've gathered mine from trips to Marshall's, Target, thrift stores. I usually only get white ones, square or round. Anywhere in price from $5 to $100...just depends.
AHome goods, Marshall's, tj max, and target. Hobby Lobby had a pretty big sale not too long ago I got some fabulous ones from there.