Hey there Collok,
I do not believe it is possible to purchase this as a one time deal. Adobe went to the creative cloud, subscription based service a couple years ago. I'm not certain whether you can still obtain a copy of the CS6 standalone or not. Perhaps someone else will chime in on that.
The creative cloud is a good deal because of the ability to always have the most up to date products, though for a the one time user, that's probably not the ideal situation.
Wish you all the best.
Adobe used to sell CS6 standalone up until about a month or two ago. I understand them stopping because some of the software in CS6 was having an increasing number of issues on modern computers (which makes sense considering how old CS6 is).
So, I'm afraid you will have to get it via subscription. Now, you can pay a whole year's worth of subscription in one go which is kind of similar...
The good news is that you will be on the latest version this way and you get all the lovely new versions of the software, plus you get TypeKit, plus you get neat features like Libraries that sync with the mobile apps (and I LOVE some of the mobile apps), plus you get...well, you get the idea.