Where and how do you obtain the SPIRIT CAMO?

You get the spirit uniform after defeating the Sorrow.
You have the area where you walk down the long river and you have to shoot the sorrow to defeat him. After you die at the end and use the revive pill you start in a new area and you'll have the spirit uniform in your inventory.

The only way to get the spirit camo is to go all the way through the sorrow boss battle. He can't be killed so just keep moving and shooting the ghosts is pretty fun. But yeah, to spoil the end what happens is, the sorrow dissapeaers and the ghost stop coming, you will see the sorrow hovering above a weird body or skeleton thingy hunched over. You can shoot them but nothing will happen, so just walk up to it, you will die and at the screen where it says snake is dead, go to the inventory and select revival pill. If you die at any point of the game from the sorrows Beam or from the ghost eating your soul, you can still do the same thing with the revival pill, actually the first time I beat the sorrow, I just died half way through and I still got the camo, it might have been a glitch becuase I bought used, which sucks.

You don't even have to walk through the boss battle with sorrow just try to swim and kill yourself and take the revival pill it's alot faster especially if you killed alot of people I know from experience.