I agree with jlhewes about calling Dimensions for more floss. They are good about their customer service. I have done several of their kits, and never had any problems. You can get a floss conversion chart for DMC to other flosses at Cyberstitchers.com., but I never mix flosses. You just can't get an exact match.
I too have searched my house for floss that has gotten lost. I have found it in some of the weirdest places. It seems that my body is a magnet for floss. LOL