The one I found listed at $17.95 just came up on the list of search results, but the page won't open, so it may be out of date. The listing was for City Models, which, from what I can find is in Perth, but as mentioned, the web page doesn't open, so I don't know if the shop is still operating. I did find a phone number listing, (08) 9321 4339 so you might wish to try that and see if you get an answer.
Stanbridges in Perth carry Sparmax spares, but don't currently have the 0.3 tip listed.
As far as the different branding goes, it does not surprise me. Badger and Iwata brushes can be found under different brand names too.