I've been using one of these for about 15 years.  The pick up tube for the paint needs to be changed to copper or brass, other than that it has worked well.  Some parts and bottles are available at the local Hobby Lobby.

http://www.tcpglobal.com/PAS-H-SET_2.html?sc=113&category=3601391#.VnMzYP1Ihpg

a good "entry level" airbrush that will serve you very very well forever, and has parts available, is the Paasche VL
its been around for decades,, and is extrememly well suited for modeling

here is a quick google
https://www.google.com/search?q=paasche+vl&ie=utf-8&oe=utf-8

Yup, can't beat it for the money. I've had mine for years now. Works perfect every time.

This one got great reviews from someone on this forum but I can't find the thread.  I bought one but haven't had a chance to use it.

http://www.harborfreight.com/deluxe-airbrush-kit-95810.html

IWATA  eclipse
  it's the work horse of  the custom paint world

its also like 150 bucks,, the VL can be had for half that,, and is for the intents and purposes asked about, certainly viable,,

the Iwata is a great brush, I have both,, I grab my Iwata mostly,, granted my Iwata is a bit further up the pay grade,, but My VL gets used whenever I want to spray areas as opposed to small lines,, or for tshirts,,
I still stand by the best answer for the OP question is the VL,, I cannot in good faith recomend the Harbor Fright gun,, they are just to inconsistant

fair enough,, we all have our own opinions, I was actually expecting someone to beat me up about my comments on the Harbor frieght gun,, it usually happens LOL

Rick I see most have recommended good airbrushes and my vote is also the VL

I have to add they are only good for very fine and small detail, not any large areas of fill

You mentioned a camo paint scheme and perhaps you might like to use a 4oz finish detail air gun instead of, or in addition, to an airbrush

These can range from $400 down to the very good for the price Harbor freight version for $19~$49....Sparky has a video of the HF el cheapos

I have several of the different sizes of HF paint guns and for the price they do as good a job as my much more expensive Binks detail guns ( I used to custom paint cars and motorcycles)

There is a technique for using foam shapes to soften the lines from one color to the other color... if that is the effect you need

typical masking will leave a sharp line between colors and some schemes are like that. But for soft lines between colors the mask is tall off the surface and painted from behind the line leaving a soft transition.  I use closed cell thin foam 1/8 to 1/4 thick  found in some packaging I save for this use. I cut to shape, thin layer of rubber glue and set in place