I am so confused. Where do I find these creatures; Gloop, Snorker, Pink..

It's pretty simple. Just go to the egg shop and buy an unknown egg that doesn't use berries.
You'll just have to keep trying out new eggs and see what creatures are inside. Tuckles are pretty common so you'll their eggs a lot. A Gloop and Tuckle are water monsters, Perisnicket and is grass and Snorker is earth type. Earth type monsters are fairly uncommon and don't show up as often as water or grass type monsters. They are also a bit more expensive so it would be wise to buy an earth type monster and then make multiple eggs for later or to gain extra coins. I doubt there is an actual cheat that would allow you to find a specific monster though. Happy Searching.

The best thing to do is wait until new stock arrives in the store. Typically, if these are requests for customers, the egg that satifies a customer's request will have an "!" above it. You can then buy it, incubate it and grow it. None of these monster eggs require monsterberries to purchase. It just takes patience in getting them. Color request monsters can be easily achieved by using special food or dyes. Consistent breeding to get the colors you want is not necessary with the foods and dyes, but will work but it leaves you with more monsters of the same breed than you know what to do with so use of special food and dyes is best; it also saves you money. Dyes and special food can be aquired by playing the monster mini games, getting the tickets and using them in the spin machine; last icon on tab bar while in shop. The gloop eggs have 2 vertical stripes going down the egg, thats how you can identify those. Persnicket eggs have a zig-zag pattern at the top, tuckle eggs are the ones with a curl pattern on the egg, and snorker eggs have many lines with one large circle at the base of the egg. All of these eggs are generally cheap and easy to care for, with quick incubation times. Hope the two combined answers are helpful.