So far for this year all of the Pulp Alley scenarios of the month are listed as solo compatible.
For Tomb of the Serpent there is a minis list at the start of each chapter which basically adds up to 1 x Shadow of Chaos, 1 x Shadow of the Burning Desert, 3 x Priests, 4 x Faceless, 4 x Militant Cultists, 4 x Fierce Cultists, 4 x Insane Mobs (gangs), 4 x Abominations, 3 x Dune Stalkers, 4 x Risen Warriors, 4 x Tomb Guardians.
I do not have a huge collection to pull from so some of my minis had to serve multiple roles. I hope the list helps.