Please don't buy eggs in shops. It's a huge profit for me, but i die a little inside when i clear my inventory of eggs i've collected (some of them in the 50k range). You cannot purchase any pets above 9* in the player market.
There are collection folders that allow you to upgrade your pets to 10 star (3 of them i think).
You can upgrade wanda to 10* jenga from there and it's honestly the only pet you need in the game maxed out right now.
The rest are drops. for any UQ, or expedition/subquest view the quest log and item information. It will tell you what pets drop where.
12* wanda drops forest for example. There's a couple 13*'s a swell, i've only see the rappy on pso day though. I've heard people claiming to see some 13* pets drop off luther etc..but I haven't seen any.