I painted them by hand when I built that kit about 12 years ago. It's one of the 47 Ronin kits, of which I seem to recall there were only two.
Try this. For the diamond pattern on the trousers of one of them, paint the base color, a reddish brown IIRC, and then paint solid diamonds in a pattern over the base, leaving the base color only visible as stripes. When the diamonds are dry, fill them in with base color so that the only thing left of the diamond are stripes of the approximate thickness of the distance between the diamonds. Then you can free hand whatever little pattern in the center. If you get the hang of it, you can figure out ways to replicate other patterns too. You kind of have to think in both negative and positive space, while working backwards from conventional thought.
Here's another trick. A few guys I used to know from my old figure modeling club used decals to lay out a very basic pattern, and then free handed over and around it. It worked very well for Tartans and heraldry. The decals will flow naturally over the folds, which is the hardest thing to replicate free hand, and then they could paint right over the decals and move beyond the basic pattern they provided. They don't even have to be in the right color, since you'd be painting over them, and then you'll have painted a perfectly aligned pattern over the compound curves of voluminous garments.