Have you tried townandcountrypumpsandpipes.com.au? Or some local boat chandlers?
Alternatively you could buy a 1/2" BSP lefthand thread die or dienut (you dont need to buy a wrench if using a dienut, you can use a spanner, but it doesn't adjust so cutting a good thread on steel can be a bit difficult sometimes) and some brass (as it easier to cut a thread on brass than stainless steel)
The brass needs to be 20mm diameter, cut a piece off about 50mm long maybe and then cut a square shape on one end say 20mm deep. Then you can clamp this in a vice, and cut the thread on the other end. Not sure but you may even be able to get a lefthand tapered thread die. Otherwise, if you can only get a parallel thread die, just use PTFE tape or Loctite 55, if you have that down under, to seal it. If you want to be really clever you could drill a small hole through the square end and thread a cable or string through it so it's not lost if you have to take it out.
Alternatively you could buy a 1/2" BSP lefthand thread die or dienut (you dont need to buy a wrench if using a dienut, you can use a spanner, but it doesn't adjust so cutting a good thread on steel can be a bit difficult sometimes) and some brass (as it easier to cut a thread on brass than stainless steel)
The brass needs to be 20mm diameter, cut a piece off about 50mm long maybe and then cut a square shape on one end say 20mm deep. Then you can clamp this in a vice, and cut the thread on the other end. Not sure but you may even be able to get a lefthand tapered thread die. Otherwise, if you can only get a parallel thread die, just use PTFE tape or Loctite 55, if you have that down under, to seal it. If you want to be really clever you could drill a small hole through the square end and thread a cable or string through it so it's not lost if you have to take it out.