I am not trying to put you off hand painting but a small airbrush type spraygun like these on ebay cost less than a packet of decent paint brushes. The spec on this one is that it has a 50mm spray pattern which seems perfect.
http://www.ebay.co.uk/itm/Spray-Gun-...item46072cc0a9 If you dont have a compressor get a big old lorry tyre , they pump up to 120 psi and used to serve me well in my youth for spraying all the old motorbike frames and tanks, they hold enough air to get round something like a chassis. Just cobble up an air line of the valve and away you go. Kev used an air brush on his chassis.
Bob