dont bother. whatever picture you find will never beat imagination.
So just go right ahead and describe in words the overall description of the orc and throw in some detail and let the player's imagination do the rest.
pictures/figurines/maps and anything remotely related to fixed descriptions ruins alot of the fun.
I rather imagine myself what that Ork security guard with a smelly breath and a earring wearing ARES logo kevlar tshirt looks like than to have some half-ass attempt of apicture to show a fantazy ork with a cleaver.
Im not an artist so I cant draw what i imagine so i just simply imagine more
no picture can ever match imagination. it can only restrict on what your want to do..
In RL my appearance changes weekly (or forthnigtly depends on when i decide to shave my beard) so there really is no "average me" and having a Ork picture to represent your/your PC character will not do anyone good.
dont limit yourself with snapshots in time...just imagine what ever you want an ork to look like...
if that is still no an answer you can try search for warhammer 40000 and visit the many websites dedicated to the hobby and just pinch some pictures from their pages.