"Your questions don't bother" (that is a rough translation of a sign that can be seen in many stores here)
Most Pokemon can be found everywhere, but there are some of them which are "regional", meaning that they only appear in specific areas of the world. That said, some pokémon that according to internet are regional have appeared here (I have them), which I guess happened in specific events. Same is true for some pokémon ("legendary") wich are very difficult to see.
Players can trade other pokemon with other players that they have previously befriended (which is a thing, you befriended someone and can send them a gift each day. The more gifts you exchanged with your friends, a better friendship you have and that gives you and them some special bonus.). You can also fight your friends' pokemon and get some awards for that. But the problem is that you can only trade with your friends when you are physically close to them. That means, I can do a combat with Wardenferry, who is in USA while I am in Argentina, but I can't trade with him.
So, my only way to get the particular Pokemon I was discussing was traveling to Australia or befriend somebody who has been in Australia and has several said Pokemon to exchange with me. Not very probable.
Your level is raised by winning points, and you do that many ways: catching wild pokemon, hatching a pokemon egg (what you do by activating the hatching and walking. Some eggs need you to walk 2km, other 5, 7, or 10. The eggs that need more walking to hatch have a better chance of giving you a better pokémon), winning combats with your friends, winning combats in pokemon gyms (where you fight the pokemon that players you don't know have left there) and doing raids, which are things you can do alone or with other players (not necessarily your friends) against a single pokemon who is normally quite powerful.
Now, the gifts you send to your friends are random (I mean, not the sender not the receiver knows what is inside until the gift is open) and they include points, potions to heal your injured pokemon, and, eventually, an egg. I THINK there is a chance that if I befriend someone in Australia and they send me an egg it can hatch an Australian pokemon. But I am not sure and I don't have any Australian friends, though.
If you need more details, I am ready for answers (I left a few details out)