Starters and other pre evolved monsters would be more sighted in the wild than their final stages, may find nidoran in forrests around rural areas but nidoking would only be sighted on mountain terrain and in caves Same goes for zubat, you'd find low level zubat absolutely everywhere, attics, trees at night! but golbat would only be found in caves around actual mountains with crobats being found deep in the lower levels
the basic animals people see are small birds (pidgey, spearow, hoothoot) rodents (rattata, pikachu, sandshew)
The deeper you go into the wild you would pehaps find the further evolutionary forms, places on earth with more wildlife = more pokemon of higher levels you would find.
you would find pidgey at a park in the city, but would find pidgeot way out in the plains, high mountains and deep forests/woodland
basically with nature, if you go looking for trouble you will find it
The u.k and northern europe would only really see a lot of pidgey rattata spearow sandshrew and bug types, perhaps an ekans or two (very low level small in size and would never climb the food chain enough to have wild arbok) Koffing weezing would maybe be found because of the old smoke stacks from the industrial era. maybe a few grimers in the river thames. Anything that can deal with plenty of cold rain and less sun light than other places (dark type pokemon and night time dwellers like murkrow would perhaps be more predominant in europe) Lapras is based on nessie, so lapras would naturally be found in cold parts of the world and caves Dratini is a rare monster indeed but still has the same characteristics as an eel Plus I always thought dragonair was based on an oarfish and these creatures look very much like the old sea sepernt paintings So in theory most of these types of myths are centered around these Dratini would be found around the pacific oceans and up around japan Ghost pokemon would be found anywhere on the planet to be fair
unlike the anime and games a trained gyarados would only be the way you'd see it in small bodies of water
they are known for violent rages (thrash, dragon rages, hyper beams)
so it's certain any of them in the wild within a few miles of civilization would have been hunted down.
magikarp found anywere even near citys would forever stay low level.
take a minute to think about actually training a gyrados in real life, a pitbull would chew a babys face but a lv 30 gyardos would bring your entire house down in minutes lol
a trainer would have to had many years training a pokemon like this to let it out its pokeball in shallow water to show people or even get medical attention without a fit of rage
plus a real life gyrados wouldnt be able to fly! so training them like an onland water type (marill) would be difficult.
With the way I put this post across Ultimately most average pokemon battles would see a lot of rattata, pidgey etc because you would literally have to risk your life to capture most of them, you wouldn't go to india and kiss a wild cobra just the same you wouldn't kiss a wild arbok