Derick and Geoff, oh and Roger too. 

I finally got a look at these things. I've finally figured out what the deal is. My work network uses Websense to control site access. Imageshack has been tagged as a no no and it blocks anything that is hosed there. 

Thes ovens are just awesome!!! Not something you typically see here in the states. Hard to say who made em as the markings provide no hint because I've never seen em before. One thing for sure is they are probably old. Typically, it is my opinion that these camp style or DO's w/ legs were not the lifes blood opf a foundry and the #'s made were not as great in comparison to a regular DO w/o legs. It cost a foundry money to cahnge patterns and I don;t hink they did it on a whim. Depending on the foundry I suspect they didn't make a huge volume of these and the patterns lasted into the later years. 
To better explain that let me use Galsscock Foundry as an example. Typically if something has a sprue mark it is considered very old. A sprue is a round(ish) mark where the iron flowed into the mold. A gate mark is a line or slash looking mark where the iron entered the mold. Now any and every piece has a gate because you got to pour it from somewhere but the next step in the evolution was to move the gate up to the side or rim which eliminated that nasty scar looking mark. We can talk about why they did that but for those of you that have been around awhile, you already know some of my theories. In the states, the general rule of thumb is that around the turn of the century (1900) most foundries had or were in the process of switching to the side gate. Now back to glasscock, Nollie is quit sure, due to his extensive research into his families foundrythat for the spider and campovens that they continued to use the bottom gated mold into the 1940's. Now speculation leads me to believe there was no need to make a smooth bottom on something that was not intended to sit on a stove top. The gate mark didn't matter so there was no need to buy another pattern. 

I told you all that to tell you this, I believe these are old. Rule of thumb for most pieces is if it has a gate you can figure 1900ish or before but as I explained above   they might not be that old. Best I can guess is 1940ish or earlier to as early as 1870 maybe, but I don't think there that old. I think Roger probably nailed it with an early 1900 ish or maybe teens.  The last picture throws me with that round mark. Is it a sprue or a bump? 
There are other age indicators as well, including a squared off or triangle leg indicates their older. the ears (on the two I can tell) are the typical 7 shape. I'd love to see some better pictures of the ears on the one. It looks almost squared off w/ the bail entering it from a 90 degree angle to the oven. With that exception I thing we are still safe in assuming early 1900ish. 
Lastly, I really can't nail origin but I do have some opinions. Although I've been to Sydney Australia and all over new Zealand I didn't get to look at your Iron cookware and am certanly no expert on the continents foundries, common sense tells me the oven got their one of two way's. They were either made there or imported there. Regardless of how they got there the do have some design tendancies that lead me to believe they have some french influence. Another rule of thumb is the concentric circles on the lid are typical of a French piece although these are more ornate than most. Other than influence, I'm sorry to say there is not much more to comment on as far as origin. 

There are many fine pieces out there in the same catagory as yours and short of running across an old catalog that makes ties to a manufacturer or retailer it's really hard to nail down unmarked pieces. 
These pieces are really good example and  I thank you for sharing them with us and if you every decide to part with them keep us in mind. 

I'm looking forward to Joel's assessment, Joel? Where's Joel?