@Tapirlord I could see T nuda as well, though I'm used to seeing the post anther lobe being more "pinched". VicFlora has a very good diagnostic for species in this complex.
Following the key it seems Vicflora would seperate T.arenaria from T.nuda based on size of the perianth segments. Luke, roughly how large were these flowers?
I distinctly remember the flowers being quite large from memory (probably a few cm total diamater) - they seemed larger than I was used to for other Thelymitra at the time.