I think you're missing out by not going with CC. Not only are there some really nice features introduced since CS6 (and really solid performance through CC 2014 on my Windows 7 machine), but you miss out on TypeKit, Libraries, and the interplay of the mobile apps (which are underrated, in my opinion). I work a lot faster even in the first CC version of AE (12.2) than I did in CS6.
Remember, a Creative Cloud subscription gets you access to CS6, CC, CC 2014, and CC 2015 too. So you can use whatever works best on your system.
If you really, really want to buy CS6, you can do it by calling Adobe according to this page. I believe the number is 800-585-0774 if you're in the USA.
Don't expect it to work on every newer operating system either. So, if it works, don't update your system!