I have a small update to give you, the Panzer 58 only will appear on EU and NA.
Our Russian comrades who are accustomed to be spoiled have been complaining about it on their social pages. Although I'm from the opinion that exception from China every server should receive the same vehicles, that's not the reality of things and is about damn time that EU and NA get to receive some special treatment!
Edit: Last time Wargaming spoke about this vehicle its was marathon reward, check what I posted earlier on the blog: http://goo.gl/YM74hZ.
Ectar (a community manager for EU/EN) has said today that there wont be a marathon mission for the end of the year, I believe because is too close to the Action X marathon, check Q&A: http://goo.gl/UMx9sz
Second Edit: for those on the SEA server complaining in the comment section, last time I heard you will be the only ones getting the Patton KR, this information came from one of the WG RU official pages. (And please go to your settings and enable people to answer to your comments, thank you.)
Panzer 58 in Thun