Hollis ATC cumberbun extension available?

I just recently purchased a Hollis ATC XL and upon receiving it found that the cumberbun did not fit me, I located the zipper compartmant in the back that allowed the two seperate pieces to be extendedto their full ability. But that only made it possible to close the cumberbun while wearing my street clothes not in a full drysuit So my question is, is there a larger XXL cumberbun or an extension that I can get to have this work properly?

Thank you in advance
Jeff