Hi lachlan, sorry no ones replied till now, you might want to try the international section of this site, and not just the Australian section. I post in both.
In regards to your questions, I've had luck on
Free Local Classifieds Ads from all over Australia - Gumtree. The great thing about gumtree is that you can post want you WANT - not just what your selling! Hence, if your after something rare - gumtree's probably your best bet
I'd imagine eBay would be pretty good as well. You've mentioned
Used Cars - New Cars - Search New & Used Cars For Sale - carsales.com.au but i personally find them a bit too expensive, and the trading post on line (there's not printed edition any more). I haven’t bought from the trading post in about 10yrs, but they used to be pretty good
Trading Post - Online and Mobile Classifieds
In regards to grey imports - i personally would stick way clear of them mate. if you buy a model that was officially brought out in Australia, you know exactly what the specs are etc, but even with grey imports of the same year, odds are, they will be slightly different, and it'll be nothing but headaches. 4Runners/ surfs aren't exactly the same all over the globe. Just like with any car that’s sold world-wide, there are often minute changes and modifications or versions for each continent and market. And if the parts aren't found here, it will be more expensive to have the parts shipped over.
Hope this helps! and if so, please consider pressing the 'thanks' link!
Cheers, Ben