Cath and Tony, MattM and I visited this site today and found some of them shriveled up and past their best, like this one: http://canberranaturemap.org/Community/Sightings/Details/1948166 But they look much smaller than O. hamatus in the flesh. Much smaller and lighter/weaker build, I am wondering if this sighting is not actually O. hamatus and could be O. aciculiformis?
I'm inclined to agree with you Aaron. O. hamatus tends to be a somewhat more stocky looking plant. The free points on the lateral sepals are not as curved and hooked as in O. hamatus.