The DMT XXC is the one I recommend for stone flattening. It works wellhttp://www.chefknivestogo.com/dmtextracoarse.html
We should have more Ozuku koppas in a couple weeks. I'll email you when they are available. They usually sell fast.
I'm not sure about the manufacturer of that steeel.
I just started a new forum for Chefknivestogo. Do you mind if I use your question and my answer? It will help others who read it. I'll only use your first name if I post it.
SRS-15 is good steel. I'm not sure who makes it. Here is a look at the composition: http://zknives.com/knives/steels/srs-15.shtml