You can get some on Amazon if you just search for floss bands. I have a pair from amazon, and have used them on and off for 4+ years and haven't had any issues.

https://www.amazon.com/WOD-Nation-Recovery-Flossing-Increasing/dp/B00YE4J63K/ref=sr_1_1_sspa?keywords=floss+bands&qid=1564764208&s=gateway&sr=8-1-spons&psc=1