The adventures we’ve published so far that were intended for TOS include:
Standalone PDFs available on DTRPG and Modiphius.net
Remnants
Hard Rock Catastrophe
A Forest Apart
Contained within These are the Voyages
A World with a Bluer Sun
Contained within Strange New Worlds
Plato’s Cave
Drawing Deeply from the Well
No Good Deed
Whole of the Law
The entire TOS-era half of the living campaign
All of the other adventures we’ve published include guidance on how to adapt it for use in other eras, including TOS, so with a little work, almost any adventure can be adapted to TOS.