Difficulty in finding a white metal, mechanical Louis Cartier Tank?

[sydneysider]

I've fallen in love with the white metal, mechanical Louis Cartier Tank's. From what I've discovered so far there aren't too many examples:

* Some automatics ("Jumbos") made made during the 70s in white gold;
* Some platinums made between 1998-2008 in the collection ‘Privé, Cartier Paris’
* Some platinums made prior to 1998 (not got much info on this)

I have a few questions I was hoping help answering:

1. Are there are other models? (is there any good sources online of this information)
2. How hard are they to come by?
3. How much should one expect to pay to secure one (ballpark)?

Thanks,
Graeme