Dard Divorce is a pretty fun one.
They have one copy left here,
http://www.diabolikdvd.com/search/se...Dard%20Divorce
It says PAL all region though so I'm not sure if that's exactly region free, I know the copy I own isn't.
If you like Ittenbach you should also check out "Garden of Love", it's called like "The Haunting of Rebecca Verlaine" or something along those lines here in the states. If you liked "Das Komabrutal Duell" I'm sure you would like any of Ittenbach's films. His most recent "No Reason" can be ordered pretty much anywhere online, think it was even on Walmart's website for a while.
Then of course there is Jorg Buttgereit who did, "Necromantik", my fav from him is "Der Todesking" which I believe you could pick up from Diabolik last I checked.
The film "Cannibal" by Marian Dora is one you'd like too, as long as you don't mind dicks in every other scene, difficult to find though. I recently picked up Melancholie der Engel by the same director, it's only in German though so I'm taking my time on getting around to watching it.
I've also recently ordered a lot of movies from Dtm.at (yes that's the actual website) but you'll need to pick up a region free player if you want to watch most of those titles.