I have seen them listed on eBay Australia occasionally. But during Covid in Jan 2021 and wanting to get projects progressed while I had some down time I just used a USA supplier via eBay, sounded like it was a Corvette parts supplier who had them in stock. Airmail posted really didn't cost that much.
Caution: Just be careful you get the right pair of kits! Ask me how I know... The '70 to '72 is one set, whereas the '73 is different (as in my case, which I eventually deduced after finding out that my carbs were incorrectly kitted with the front one running very very rich). On a '73 the front carb fuel intake valve is a different length/casting height to the one on the rear carb. A Nissan tweak for something to do with the tilt of the engine, apparently, from what I read online.
My 2c worth. Hope that helps some.
PS. Just checked my purchase history, Including postage ex USA they cost round about A$90 with the then exchange rate.