The only thing you could do is search some independant sites for the older ones. I'm sure you may find some on EBay as well. I found this specific site where there's a guy in the Miami Florida area where he has all of the DVDs you're looking for except XXVII:
http://www.blujay.com/?proview=50&pa...at=0&keywords=
Here's a list of all the sites, well not literally all, of ones with XXVII:
http://www.google.com/products/catal...ed=0CGQQ8wIwAA