if not already tried, suggest texture creation tool Genetica; go here:
http://www.spiralgraphics.biz/index.htm
They have a "paid" version which adds much capability but also a free "viewer" (does more than just look)
and you can download several free "packs" of stuff...most recent is plants & medieval
Sign up for free notice of new stuff
I've had it for years and its a useful addition to any 3D...and even 2D.
Just remembered not everyone may know about it.
They also have a free "wood workshop" to make wood textures.
All based on procedural math; not picture images...but you can make pictures to use in TFP