Posting an updated answer since the old one is outdated. For a regularly up-to-date list of available Pokemon, see Bulbapedia.
Kanto Pokedex. All Pokemon are obtainable.
Jotho Pokedex. All Pokemon are obtainable.
Hoenn Pokedex. All Pokemon are obtainable.
Sinnoh Pokedex. The unobtainable Pokemon are:
- Rotom Fan form (base, Frost, Heat, Mow, and Wash forms are available)
- Phione and Manaphy
- Arceus (all forms)
Unova Pokedex. All Pokemon are obtainable, but some alternate forms are unobtainable:
Zen mode Darmanitan (Unovan and Galarian, base modes are available)
Kyurem-Black and Kyurem-White (base form is available)
Keldeo Resolute form (base form is available)
Meloetta Pirouette form (Aria/base form is available)
Kalos Pokedex. The Pokemon listed below and their evolutions are unavailable:
Honedge
Volcanion
Alolan Pokedex. All Alolan forms of Kanto Pokemon are available. The Pokemon listed below are unavailable:
Wishiwashi
Mudbray + Mudscale
Pyukumuku
Type: Null + Silvally (all forms)
Minior (all forms)
Mimikyu
Dhelmise
Ultra Necrozma (other Necrozma forms are available)
Magearna (both forms)
Zeraora
Galarian Pokedex. The following Pokemon and their evolutions are available, in addition to all Galarian forms except Corsola:
Grookey
Scorbunny
Sobble
Skwovet
Wooloo
Obstagoon
Persekker
Sirfetch'd
Mr Rime
Runerigus
Hatenna from 2024 Sep 18
Falinks
Stonjourner
Dreepy
Zacian (base form only)
Zamazenta (base form only)
Zarude (base/non-Dada form only)
Regieleki
Regidrago
Hisuian Pokedex. The unavailable Pokemon are:
Basculegion
Hisuian forms for Lilligant, Zorua + Zoroark, and Sliggoo + Goodra
Enamorous Therian form (base form available)
Paldea Pokedex. See this list for available Paldean Pokemon. Paldean Wooper is the only currently available Paldean regional form.
Unknown Pokedex. All Pokemon are obtainable (Meltan and Melmetal)
Many of the obtainable Pokemon can't currently be caught, for example most legendaries. If starting now, you'll need to trade with a player to obtain these Pokemon. Unfortunately Mythical Pokemon other than Meltan and Melmetal can't be traded. Mythicals that aren't currently available cannot be obtained until they became available again. Fortunately Mew, Celebi, Jirachi, Victini and Shaymin are available through special quests without a time limit. Hence the unobtainable Pokemon that have previously been released are:
- Deoxys (all forms)
- Darkrai
- Keldeo (base form, requires purchasing a Something Extraordinary Ticket from 6th to 11th Dec 2022 and completing the Special Research)
- Meloetta (Aria/base form)
- Genesect (all forms)
- Diancie
- Hoopa (all forms)
- Marshadow
- Zarude (must have started Special Research quest from 1st to 10th Oct 2021)