Peter I think it is not common; I have seen many Wax-lip orchids particularly in this area but never a 2-flowered specimen. Cath found a triple flowered Canberra Spider orchid the other day, which attracted a bit of discussion, see http://canberranaturemap.org/Community/Sightings/Details/3360982 (ignore the locality bits; this has been solved.)
I have seen 2-flowered Glossodias from time to time, but they don't seem to be very common. This reminds me that a plant I have seen locally with two flowers in the past only has a single flower this year. This might go towards answering Aaron's question about whether the 3-flowered C. actensis would always have 3 flowers that is in the comments for the sighting referred to by Waltraud above.