I've found two places that sell them, or at least something like what you are asking for
http://www.foundationsofwar.co.uk/products/00156-round-ships-decking-bases.html
http://www.back2base-ix.com/timber-p20.html
I've not used or heard of either of those companies before, so caveat emptor etc.
I'd just make my own, plenty of options.
Find some wood textured plasticard shaped with a circle cutter.
Use the roller from greenstuff world that Desubot mentions.
Thin balsa strips cut to shape.
Carve or sculpt your own.
Depends on how much effort you want to put in.
Edit: Just found this:
http://newartways.com/en/step-by-step-how-to-paint-wood-on-plasticard.html
You could even paint the wood effect on plasticard strips