Can I use Thorton to put a non-Dark Basic Pokemon from my discard pile onto my bench if I have Eternatus VMAX with the "Eternal Zone" Ability in play?
No, you can't play Thorton at all if there aren't any Basic {D} Pokemon in your discard pile.
Source: TPCi Rules Team (2022-09-29)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH3_117
SWSH3_117
SWSH11_167
SWSH11_167