This might have been covered here before, but I couldn't find it in the first several pages of this topic. I posted this in Car Kit Reviews in reference to the new kit thread on the '49 Mercury woody wagon, but I thought it would have wider application here.
A DIY suggestion -- If you download wood pattern samples from wood supplier websites, you can use them as is, or put them into a graphics program and adjust the color, sharpness, size, etc. any way you want and print out on paper or decal paper.
Here's how I find what I'm looking for:
Just a few examples.