I have a 10'x10' Kodiak Canvas Flex Bow tent. I purchased a heavy-duty coated canvas groundcloth from Springbar tent out of Utah. Springbar makes a great 10'x10' tent, and they have a groundcloth designed for it that is 9'11x9'11". It fits perfectly under my tent.
I was trying to post a link to the groundcloth, but Sprinbar's website doesn't seem to be responding. Here is a link to their website. Maybe you'll have better luck than I did navigating it:
Springbar 
