It seems like your budget isn't unrealistic, although I don't know how much shipping will run you. You've got a fat $2000 USD - think around $1000 for the kit, $800 or so for the build, and a couple hundred for the ride. I would say call or email around and line up the gunsmith and the kit provider to determine availability, timeline, and cost. Make sure your gunsmith fully understands this kind of build - I'm sure there are fewer Aussie gunsmiths who do this kind of thing than here in the states. As I'm sure you already know, building a kit like this isn't the type of job your average gunsmith does.
As others mentioned above, Pecatonica River Supply and Clay Smith offer French Fusil kits. R E Davis also offers a kit on their website, and I've heard good things about it. Track of the Wolf isn't showing their Tulle Fusil de Chasse kit right now, but they're showing the parts, including precarve stock. I'd contact them to see if they'll put a kit together and for how much. Tennessee Valley Muzzleloading also offers a kit and a completed gun for $1850 USD. As far as authenticity goes, I'd assume Clay Smith does the most accurate of the choices here, perhaps followed by RE Davis. Of course Smith's is the most expensive.
As I mentioned, contact each seller for availability - like Rich pointed out, a lot of parts are in short supply at the moment, so just because a kit is advertised doesn't mean it will be available any time soon. Many kits are carved to order, so check timeline.
I'll briefly address your comment about costs and the future of traditional muzzleloading. You have a valid point. I'm also a father with young kids and understand well where you're coming from. I think there's a place for mass-produced guns like Thompson Center and Pedersoli produce. I also think there's a place for semi-custom guns from higher volume hand-makers like Tennessee Valley Muzzleloading and the late Tip Curtis. These guns offer various tiers of historical accuracy and handling characteristics that are reflected at their price points. (Finally, there's the unique niche occupied by Kibler kits,: historically accurate, easy-to assemble kits for the beginniner - but they don't make the style you want). But the fact is, building a well-made muzzleloader by hand with attention to detail and accuracy takes materials and time. I think that most gunmakers sell their work at a price that, if broken down, would result in an abysmally low hourly rate. Many do this to make a living or to supplement a living. It's just not feasible to expect that kind of work to come cheap.
With that in mind I'd urge you to consider the TVM Tulle Fusil. If you're just getting a kit, I'd perhaps consider the Pecatonica or Davis kit first (or, if you can make the numbers add up right with your gunsmith, the CLay SMith kit). TVM gets a lot of criticism for not being as historically accurate as full custom builders, and also for leaving too much wood on the stock. However, they produce a good functional gun and are, in my experience, decent people to work with. I've emailed Matt Avance a few times, and my friend bought a gun from them that he's very happy with. I had a secondhand TVM rifle for a while that was attractive and shot well. For $1850 USD they'd make you their version of a Tulle Fusil de Chasse in probably about a year, give or take. It'll be attractive and functional. The lock will be high quality. They could make it any length you want and you could discuss any other considerations with Matt. These might change the price somewhat. If you're up for doing the final finishing yourself, you could save $100 USD by getting it "in the white" (unfinished).
I think walnut is a cost upgrade as well, unfortunately. It's built in to the cost of the clay smith kit at $1150.
TVM isn't going to give you the nicest, most historically accurate gun, but I think they have their place. It's worth contacting Matt to see what he can do about timelines and his cost for shipping a completed gun down under.
I guess I don't know if Oz has any funny restrictions about importing a completed muzzleloader (or even a kit!). You might already know, but I'd be sure both you and whoever you're buying from should make sure you know all of the red tape before you commit!
Good luck!
