cdnn had some steyr factory 1 piece picatinny rails that were heavy duty and high quality. Unfortunately, I think i bought one of the last ones so u should give em a call.
I think they were amde by EGW or some other high quality company, I can't remember for the life of me.
I believe Steyr is using/recommending Talley Manufacturing, Inc. rings and mounts. They do have a one piece picatinny, which I'll probably be using on my new 7mm rem mag SS pro hunter.