I realize that I run the risk of looking like someone with way too much time on my hands but cute thumb tacks are hard to come by. When you can't buy it, you've got to make it. This is where my fabric samples come in handy...again.
Fabric stores sell button cover kits that are perfect for making your own. The dome and back are all you need for diy buttons.I started by using pliers and removing the silver thingy that would allow you to sew the button to clothes.
Using the template on the back of the kit, cut a circle of fabric from your favourite scrap fabric.
Lay the fabric on the white attachment device which is provided with the kit.
Pop the button out and hot glue a thumb tack to the back.