You could also do it the same way they do gun stocks with the realtree camo, or specialty decals on snowboards, etc.
I'm not totally sure how the process works, but a water soluble decal is submerged in water or some liquid bath, then the object you want to apply the pattern to is dipped into the solution and then removed to dry.
This is one site I found.
http://colorandcamo.com/
Also found this on You Tube which gives a good DIY explanation.
http://www.youtube.com/watch?v=wj6W7NQWPQo