Moldable/Printable wood-like material?
A quick search of the grand ol' internet shows that most people are recommending a wood fiber filler to be added to traditional casting material such as epoxy or polyester resin. There is a PDF available showing how to combine pecan shell flour(!) with resin and post-processing in order to generate a wood grain surface.

My search results provided a link to an Instructables comment/query with a link to the PDF noted above. I've provided the link to that page rather than the PDF, as some of the comments may also be helpful to you. The first link provided in the Instructables article is 404, dead and gone but the second one is still operational.

The document in PDF form is now a direct link and references a specific product, Smooth-on 320 resin, likely a product sold by the site hosting the document. 

The results of my search which were the most promising also referenced pecal shell flour or powder.

I suspect you will get wood-like appearance, but not necessarily wood-grain like appearance.