Last year when I thought I was going to use a set of Kooks mid length headers I went ahead an ordered an extra pair of catted connection pipes directly from Kooks. They are the regular high flow catalytic converters, not the special green ones. One of the benefits of these headers is the cats are bolt-on, so when one goes bad, it's easy to change them out.
This post is to put out a feeler if they are in demand or not. I will get them out of deep storage soon and provide pics.
Catalytic converters are not cheap. Asking $400 shipped OBO.