Hi, What a wonderful looking design!
Lanarte who sells this kit is out of Belgium. You might want to contact them at: sales Lanarte
Make sure you put in their e-mail exactly as I am showing it, which includes the space between the two words and the capital "L" since that is the way it shows on their website, to see if they can assist you with more floss.
There is a website: www.Lanarte.com you can also try and their Frequently Asked Questions section does ask what to do if you begin to run short of floss which is to contact their U.S. affiliate which is Leisure Arts. Go to "Leisurearts.com" and see if they can assist you. You would need to give them the title of your kit to see if they can assist you with it. Hope this helps.
I'm not an employee of Everything CrossStitch but one of the stitchers on this chat that saw your question!