Not sure if you want to decorate with real or not....I googled artificial twigs a nd got several sites maybe you can find something.
There called turn tables or lazy susans depending on where you get it. I have a wilton turn table that I bought from Michaels craft store using a 40% coupon , but my husband bought me a really nice one for Christmas at bed bath and beyond.
Welcome to cc and HAPPY BAKING
I know you said you want s plain round one but here's a beautiful round one. One thing to stay away is the cheap Styrofoam ones.
This is a link to a 14 inch square plateau but if you Google cake plateaus you get tons on websites with choices. I personally like Amazon just because there a well know site.