Here are Pokémon species that have some of the lowest trade volume in Pokémon Home's GTS.
Aipom
Alomomola
Ambipom
Anorith
Appletun
Araquanid
Arboliva
Armaldo
Arrokuda
Baltoy
Barboach
Barraskewda
Bastiodon
Beheeyem
Bellossom
Blitzle
Boltund
Bombirdier
Bonsly
Bounsweet
Bramblin
Burmy
Cacnea
Capsakid
Carkol
Carracosta
Cetitan
Charjabug
Chatot
Cherubi
Chingling
Cinccino
Clawitzer
Claydol
Clobbopus
Comfey
Copperajah
Crabominable
Crustle
Cryogonal
Cufant
Delcatty
Dewgong
Dewott
Dolliv
Donphan
Dottler
Ducklett
Duosion
Eelektrik
Eiscue
Eldegoss
Elekid
Elgyem
Empoleon
Finneon
Fomantis
Forretress
Furret
Gigalith
Gothita
Grapploct
Grovyle
Hakamo-o
Happiny
Hattrem
Heliolisk
Herdier
Honchkrow
Illumise
Jellicent
Kabutops
Kecleon
Klang
Klink
Klinklang
Kricketot
Kricketune
Leavanny
Ledian
Ledyba
Liepard
Lokix
Lombre
Lotad
Ludicolo
Lumineon
Lunatone
Mabosstiff
Magby
Mantine
Mantyke
Maractus
Maschiff
Masquerain
Mienshao
Mismagius
Morelull
Mothim
Nacli
Naclstack
Nincada
Ninjask
Nuzleaf
Octillery
Overqwil
Pachirisu
Palossand
Palpitoad
Passimian
Petilil
Piloswine
Pincurchin
Pineco
Pupitar
Purrloin
Purugly
Pyukumuku
Quilava
Rabsca
Relicanth
Rellor
Remoraid
Revavroom
Ribombee
Rolycoly
Sandygast
Sawsbuck
Sealeo
Sentret
Servine
Shedinja
Shiinotic
Sigilyph
Simipour
Skiploom
Skitty
Skorupi
Slakoth
Slugma
Smoochum
Solosis
Spewpa
Spidops
Steenee
Stoutland
Sunkern
Surskit
Swadloon
Swalot
Swanna
Swellow
Swoobat
Taillow
Thievul
Tirtouga
Toedscool
Toedscruel
Torterra
Toucannon
Tsareena
Unfezant
Vanilluxe
Varoom
Veluza
Vibrava
Vigoroth
Volbeat
Whirlipede
Whismur
Wiglett
Wormadam
Wugtrio
Wynaut
Zebstrika