It is likely not going to be in any stores now, being a three year old game.
The only place I've seen to download it is Direct2Drive in which you buy the game and download.
Oh, wait.
Some fansite has this... Looks like you install the SOE Station and you can download the entire game through it as though it were a big update. Trying it now.
New one, paying players cannot 'revert' to FodderSide.
And as for the installer, no go. There's going to be an official Demo for Planetside released sometime today, the only way to get in as a Reserve or so it would seem.
Hell... I just remembered that two months ago, I was able to give myself a 10-day trial key, and found it in my Hotmail. I'm currently downloading the whole client and updates through SOE. I'll be able to play for ten days as the thing says, I wonder if the Fodder will run right through it.