paints 
From Two Inches of Felt
STL (3D Model) – $5.00 USD
Includes eight different variations of a deciduous woodlands.
Easily printed on an FDM printer with no supports and 10% infill.
I usually print at 0.24 layer height and 1 to 2 line width for walls. Takes less than one hour per piece on my Neptune 4.
The scale is suitable for 6mm and 12mm as is, could be scaled to 2mm and 15mm.
Painted woods with 6mm Panzer IV for reference.