How to write the so called wooden tomato / wooden potato in Chinese (and where to find it)?
By your description I would say it's taro or 芋头 (yu tao) in chinese

https://www.google.ca/search?q=mu+shu&amp;source=lnms&amp;tbm=isch&amp;sa=X&amp;ei=J862VLp1ivxSvZODoAM&amp;ved=0CAgQ_AUoAQ&amp;biw=1394&amp;bih=827#tbm=isch&amp;q=%E8%8A%8B%E5%A4%B4&amp;imgdii=_



It can be bought in most chinese supermarkets

For more info http://www.merriam-webster.com/dictionary/taro