Node distribution is very unfavorable in zones from Cata down to Outland (since they were done with flying farming in mind, it would not make sense to have nodes very close to each other).
Best advice is to try and find smaller areas where the nodes are more concentrated ( the open world pvp areas are great, see Winterspring or Tol Barad for example) but Howling Fyord is in general the go to zone for cobalt (but expect to spend quite a lot of timr there). As an engineer, another good spot is Borean Tundra, the hot apinrg zone where the gnome robots are. There are some nodes in the caves near that spot and eng scavenge the robots for parts to use in leveling.