It isn't really rare. If you look there are actually tiny apparitions all over the area where they are found, they just don't normally spawn as pets you can battle. If go around killing all the non-battleable ones after about 15 minutes max one should spawn that you can battle.
This pet took me weeks to get. There were never tamable versions when I was questing there, and killing off the critter versions wasnt forcing capturable spawns for me as it was for other pets. I did think this was one of the more difficult wild pets to capture!