I am looking for one that holds 2 since I want to carry my two around as well. So far the only thing I have found is a bag by Puchi Bags. It has a double harness hold in it. I think they are custom made so I am sure you could have a three harness holder made as well. A bit expensive too. Here is the one I have been eyeing for a while. Good luck and keep me infomred if you find another one.
http://www.puchibag.com/images/celeb_sims_lg.jpg