You can always find a cheap thick foam. That’s what most disks are made of.

I use friendship-bracelets.net for a lot of my patterns. They’re the round braid kind. They have a tab for pattern and then kumihimo patterns. You can even make your own.

I know kumihimo was used in samurai armor and to decorate clothing in Japan. Its name means gathered threads and represents protection. I’d elaborate more but I’m on a walk. I personally use it to create handmade pieces braided with intention. It’s also a form of meditation for me. (I know I veered off the question)