Malo e lelei,
You can try importing one from Fiji.
Nagan Engineering makes them.
Note that these Fiji-style pounders are made for kava produced for the domestic market (and NZ). If you want to export to the US, you will need to specify that you want a pounder custom built, and spend a lot more money on it to make it compliant with cGMP standards. You'll need to pay extra for stainless steel for the food contact surfaces, to build a body around the machine to keep airborne dust and pathogens to get into the kava, etc.
If you can afford it, you might be better off getting a modern (rotary) hammer mill instead, but those are pricey and maybe not the best idea if you're just starting out.