For the Pokemon fans here is a list of Pokemon that can’t be obtained so you don’t have to waste your time on futility.
This pokes are not unobtainable in sun, moon, utra sun and intra moon.
You can only obtain them in trading or transferring, but then is not that easy.
List of Pokemon that cannot be obtained in neither S/M nor US/UM they are:
Nidoran-line
Oddish-line (yes not in the Alola Dex at all)
Venonat-line
Ponyta-line
Doduo-line
Krabby-line
Tangela-line
Hitmon-line
Mew
Sentret-line
Hoppip-line
Sunkern-line
Unown
Wobbuffet-line
Gligar-line
Qwifish
Shuckle
Teddiursa-line
Phanpy-line
Stantler
Celebi
Poochyena-line
Zigzagoon-line
Wurmple-line
Shroomish-line
Nincada-line
Whismur-line
Skitty-line
Plusle
Minun
Volbeat and Illumise
Gulpin-line
Cacnea-line
Zangoose
Seviper
Solrock
Lunatone
Duskull-line
Chimecho-line
Jirachi
Deoxys
Bidoof-line
Kricktot-line
Burmy-line
Combee-line
Pachirisu
Cherubi-line
Glameow-line
Stunky-line
Bronzor-line
Chatot
Spritomb
Crogunk-line
Carnivine
Manaphy and Phoine
Darkrai
Shaymin
Arcues
Victini
Patrat-line
Purrlion-line
Pansage-line
Pansear-line
Panpour-line
Munna-line
Pidove-line
Blizile-line
Woobat-line
Drillbur-line
Tympole-line
Throh
Sawk
Darumaka-line
Maractus
Yamask-line
Deerling-line
Karrablast-line
Foongus-line
Joltik-line
Ferrotseed-line
Chubchoo-line
Cryogonal
Shelmet-line
Bouffalant
Heatmor
Durant
Keldeo
Meloetta
Genesect
Bunnelby-line
Skiddo-line
Espurr-line
Spritzze-line
Swirlix-line
Pumkaboo-line
Bergmite-line
Diance
Hoopa
Volcanion
Beast Balls of any pokémon on this list are not possible
and if you want or need any of those, you’re going to rely on GTS and/or Trading Board.
The rest can be obtain via Regularly like for the shiny charm, Island Scan or Ultra Wormholes in Utra sun and Utra moon only.
If you know any one that is not on this list you can add to this and through the comment form.