There are several, for FSX models, like the A2A p-40

if you want to repaint the default FSX 737-800 you cant use the 500 or 300 model kits, for any FSX model that has a blank texture its pretty much editable without any kits, open DXTBMP go to the file marked texture (no periods on the blank white ones) and select B737-800-1-T and 2 save them as a 24 bit bitmap to the desktop and you can edit them

hope that helps