Why don't you just make your own and feel happy about it. Get an old wetsuit and cut the legs off to the length that you want. 4mm neoprene will stretch down to 3mm and that will be plenty thick enough, why not start with 5mm, that should do it.
Gaiters on the market are just not aimed at snake bite protection, there's burrs and stones that you want to keep out of your boots. Then water protection for your socks. Sure, you get condensation inside but it's not the same as water sneaking down your socks and ruining your day with crook feet. Anyone, anyone at all please tell me about any person in Australia who has been envenomated by a snake through gaiters. I will be most interested.
Grant.