After 6 and a half years of surveying, and watching the steady decline in work, and the subsequent price chopping and resulting cost cutting at all levels, I would be inclined to steer clear and go and do something else. If you want to do ag, then you may as well head straight for ag, I dont see any real advantage of flying survey lines in the interim.
However, be that as it may, here is my most up to date info on the operators I am familiar with:
Fugro Geophysics, Based in Perth now owned by CGG, based in Perth. Selling all their plastic rats (diamonds) and doing a little mag/spec in the Caravans, they also do Gravity and have or at least had a Skyvan and CASA doing Electromagnetic survey.
Fugro Spatial: Not too sure if that ended up being bought by CGG as well, they do high level stuff, Lidar, photography etc, Duke, Conquest, T206 I think.
GPX Surveys: Based in Perth, Mag/Spec Survey in 210s, although either one or both are parked with no work.
UTS/Geotech: Based in Perth, Got a new P750, 2 or 3 U206s, and 2 or 3 FU24s doing predominantly Mag/Spec with some gravity. Pretty much all parked up with no work, just a few jobs here and there.
Thomson Aviation: Based in Griffith, NSW, Mainly mag/spec, with facility to do Gravity too, 1 P750, currently in Mozambique last I heard, also 3 C210s with Mag Spec gear in. They have a little bit of work on, just enough to keep the boys going I believe.
Magspec: Perth based. New Startup company, 1 C210 at this stage, looking to expand, but at this stage no steady work, just dribs and drabs.
AAS, they have a P750 kitted out for Lidar, not sure what other systems they can fit, I think they just run it as required depending on work.
AAM: Based up Brisbane way somewhere. Lots of planes, C402s, C404s, Islanders, F406, T206, do mainly higher stuff, Lidar, photography etc. I know they pay a salary so probably one of the better places to work as most others tend to be casual.
Advance Aviation, dont know much about them but they have a Caravan out there doing Lidar at the moment. Saw it the other day.
Atlass: Know virtually nothing about them other than I had heard rumours they dont pay industry standard, had an idea they had been bought by AAM but I may have my wires crossed.
Corporate Air: Canberra Based, have a Conquest or a 404 with Lidar in it.
Thats all I can think of at the moment. The general guts of it is though, there is very little work out there right now. The companies like AAM that pay a salary are the ones to go for, as even though the other ones that pay casual day rates pay a lot per day, you could end up sitting at home for several months with no pay until the next survey job comes in.
Hope that is some help to you.
Best of luck and happy Grailhunting.