I have a cast iron three ring burner that is sufficient enough to bring a 50L boil in very reasonable time. Gets a good vigourous boil going. Very happy with it.
I have found the other burners that you guys are after in my local surplus store here-Uncle Sam's Surplus Store, Elizabeth St, Hobart. The same as the Yanks use and the same as the picture above, comes with the stand (no adjustable legs) but no reg. They are $59 but you need to have a high pressure regulator (not the BBQ ones) to get the power out of them. The stands are nice though, about the right size for a 50L keg. I have another bloke I brew with that has one, he fitted a regulator off an oxy-acetyl, it throws out the heat but by god does it chew the gas. He actually doesn't use it, instead uses his three ring burner.
Hope it helps.
Cheers
JD