I found Skull Shores at Justice but Walmart just put a bunch on shelves in several different states, mine included. As of right now the only place Create a Monster packs have been spotted that I am aware of is Toys R Us. :)
Stores like Justice, Fred Meyer, Target, and sometimes Toys R Us have a ton of S.S. Ghoulia and sometimes Ula D but not really the others. Target carries the 5-Pack S.S. and that comes with Draculaura, Ghoulia, and 3 exclusives: Clawdeen, Regular Frankie, and Cleo.
The Werecat/Witch CAM pack is veryy common at Target, Toys R Us, and Fred Meyer. The Design Lab starter is kind of common but not the extra packs. The boy CAM is also common. The only add-on pack I can find is Skeleton. The Vampire/Sea Monster and Werewolf/Dragon CAMs are kind of common. Hope this helps!
(PS this is just in Seattle, dunno about where u live. Oh and check Amazon and eBay frequently)