Just like any other Pokémon game, you will find there are version exclusives - Pokémon that just won't show up in the wild in your version of the game.
These Pokémon will be essential to your completion, so find some friends and trade the following creatures…
Let's Go Pikachu Exclusives:
Let's Go Eevee Exclusives:
If you're an experienced Pokémon GO player, catching them all will be far easier.
Version exclusives and rare Pokémon can be traded over from Pokémon GO, allowing you easy access to harder to find creatures.
Of course, if you're not a Pokémon GO player you can still start up an account and get hunting, and you'll likely find a few rewards for your trouble.
So you're just on the last few Pokémon you need, hunting for a few wild mons and evolving a few, eh? Final stretch.
If you pop into the Pokédex, you can check each Pokémon's habitat, which will highlight on your map the routes where that Pokémon can be found.
This will make rarer Pokémon such as Kangaskhan and Chansey a bit easier to locate.
Mew, Meltan, Melmetal
These three will be the toughest to find, no doubt. Luckily, it's all still possible.
First, for Mew, you're going to have to buy a Poké Ball Plus, or find someone willing to trade your their Mew. I know, a bit rough. Maybe ask your uncle who works for Nintendo.
Meltan and Melmetal, meanwhile, require Pokémon GO to access. Yep, so if you haven't downloaded that yet, best get to it. We've got a big guide on getting Meltan and Melmetal for you to read right here.