What kind of cammo? There's only about eleventy-bajillion styles.
However, if you just want the old-fashioned, non digitized cammo look, your local hardware store should carry cammo spray paint. There are a few colors to choose from; brown, beige, green... just choose the colors you like and spray them on in smooth random patches.
Funny story: We actually had a customer return his cammo spray paint because it didn't spray the pattern on right from the can! He actually had to do a (very) little thinking and even less work, but it wasn't what he thought he had bought. So we gave him his money back!