I finally managed to hit 500 pets last night. In the end it wasn't as difficult as I feared it might be but I did get lucky and get the Minfernal and Silithid Hatchling both with only 1 days of checking for them. I also bought 2 TCG pets and a Living Sandling to help me on the way. Still got some collecting and a lot of leveling/upgrading to do but wanted to get 500 done before the next patch hit and added all those new pets.
yay me!