The following forms have not had a Shiny variant released in Pokémon GO. Functionally equivalent forms are not distinguished.
TForm
psychicArmored Mewtwo
electric fireHeat Rotom
electric iceFrost Rotom
electric flyingFan Rotom
electric grassMow Rotom
psychic fireVictini
normal ghostHisuian Zorua
normal ghostHisuian Zoroark
normal psychicMeloetta Aria
dragon groundZygarde 10%
dragon groundZygarde 50%
dragon groundZygarde Complete
psychic ghostHoopa Confined
psychic darkHoopa Unbound
fire waterVolcanion
fairyComfey
rock flyingMinior
ghost fairyMimikyu
psychicCosmog
psychicCosmoem
fighting ghostMarshadow
poisonPoipole
poison dragonNaganadel
electricZeraora
bugBlipbug
bug psychicDottler
bug psychicOrbeetle
grassGossifleur
grassEldegoss
electricYamper
electricBoltund
rockRolycoly
rock fireCarkol
rock fireCoalossal
groundSilcobra
groundSandaconda
flying waterCramorant
waterArrokuda
waterBarraskewda
fightingClobbopus
fightingGrapploct
rockStonjourner
dragon ghostDreepy
dragon ghostDrakloak
dragon ghostDragapult
dragon poisonEternatus
fightingKubfu
fighting darkUrshifu Single Strike
fighting waterUrshifu Rapid Strike
dark grassZarude
fairy flyingEnamorus Incarnate
fairy flyingEnamorus Therian
bugTarountula
bugSpidops
normal flyingSquawkabilly
rockNacli
rockNaclstack
rockGarganacl
electric flyingWattrel
electric flyingKilowattrel
darkMaschiff
darkMabosstiff
grass ghostBramblin
grass ghostBrambleghast
rockKlawf
psychicFlittle
psychicEspathra
rock poisonGlimmet
rock poisonGlimmora
waterDondozo
dragon waterTatsugiri
grass ghostPoltchageist
grass ghostSinistcha
Pokémon GO: A Quantitative Approach