i'd have to agree that this was pretty misleading. reportedley, there are, not concept arts, but cgi renderings of him featured in the DK Sticker Book and movie universe guide. those are your best bets
http://www.tfw2005.com/boards/radic...055-definitive-rotf-reference-pic-thread.html Frenzy-Rumble and the other Radicons are gathering all the concept art and CGIs here. If anyone has found it, that is where to look for it.