Maybe this will give you some insight.
You must first take the knob off of the back side of the fairing. What I do not remember is where are the bolt heads that hold that bucket in the fairing (it's been a while...
If you remove the left and right side covers, you will see something similar to this on the inside of the fairing:
Those two nuts hold the housing in the fairing. In some cases, two sided tape may also be holding it in at places to.
Welcome to the forum!
Parts are available on ebay, but postage will be more expensive than the part for you, unless you can find a seller in Oz. I think that the WJ III used just the basic H4 sealed beam headlight, so if you have the bucket, you will just need the ring to hold the sealed beam...
There is just something about those springer front ends! If I ever feel the need to have something like that, this is where I am going to start...
I wonder what a Goldwing engine would look like in there! :D