I get my bottle caps from Williams Brewery as well. It is real cheap there. I also use the wooden disks as well. I just use a 1" round disk instead. It covers the whole back.
I just recently learned out to make my own. There is a lady online that made some custom ones for me and I was very please with her work. I will order more from her just because she has a huge selection and can easily find something for you. Here is a pic of my custom ones.
Just the ones of the deer.
I am using them to make our dds camo hair bows to match their camo outfits.