Cath03rize, the treasure monsters can be purchased with monster berries, however I got a copper gloop for 50 coins in the egg shop. That's the only time I've seen a new monster in the egg shop, and I check every day now. There are 4 people in my house that play MPS on different devices, and my daughter got a gold steve in the egg shop (also for 50 coins) but the others have never seen treasure eggs in the egg shop. Fingers crossed that with the latest update we'll still find them in the egg shop, even if only rarely.
For those curious how breeding works with these new monsters: First off, you can't request them, and you can't gift them either.
I wish I could - I've already discarded half a dozen gold steves because I don't have the room for them. When bred with a regular monster (for a example a squiggly gloop with a copper gloop,) the result is always a regular monster. To get another treasure monster you have to breed it with the same. Fortunately, you can do that for 1 berry in the MPS breeding center (the last option for make egg.) This results in either the same monster (for example 2 gold steves make another gold steve) OR another kind of treasure monster entirely! I've had two copper gloops make a lapis persnicket and then a gold steve and my daughter had two gold steves make a turquoise krakel.) BUT! if you raise two of the same kind of treasure monsters and then breed those together (for coins, instead of a berry, since it's in your own shop) -- well THEN I've only gotten the same monster as its parents. Tried this with 3 gold steves bred together and only got 9 more gold steves. Hope that is not too confusing and able to help someone.
I could use a horned persnicket if anyone has one - GC is chellen25, thanks!