Everywhere. I ordered mine from my local online shop through the internet. Go to www.adobe.com and indicate your country. But it is veeeery expensive! There are much cheaper programsn, but I just love Photoshop
. I am sure I do not use half of all the possibilities it has, but I can work so easily with it and it does all the tricks I need (like removal of an unwanted hand on a horse's nose ;-))
It is possible to download a trial, which will work for about 30 days. Try it. And try demos of other programs as well (Ulead Impact or Corel or so) and see if you want to spend the money. You may start by checking google on reviews of photoprograms.
Be aware that having a very good photo editor does not guarantee you make beautiful work with it. It is like having a good camera, it is no guarantee for good photos. That depends on your personal talents.
I LOVE the picture of Gelgelah. So beautifully done