You need to contact the manufacturer, Dimensions.
https://www.simplicity.com/contactus

This will take you to their contact page where you can click on "replacement part" and tell then what numbers of floss you need and the numbers of tgevfloss as well as the name and number of the kit.

Many of us have run out of floss, whikt stitching these kits. Many if us buy patterns and gather up what we need. Dimensions provides or manufacturers their own floss, which does not match other brands of floss.

I am not an employee of ECS, just an old stitcher inbthis chat with the same problem.