I went the longest time without getting one and was doing almost all of the pet dailies that I could. Then I started getting them here and there.
So far I've gotten:
Beast - used on Ravager Hatcling (breed 4) since I could never find a rare
Dragonkin - used on Emerald Proto-Welp (breed 4) since I couldn't find a rare
Magic - used on a Nordrassil Wisp (breed 5) since I couldn't find a rare
Undead - used on Sen'jin Fetish (breed 4) for fun
Critter - used on Red Cricket (breed 8) for it's kickass power
Good luck with getting yours! They ARE out there.