You would have thought so, but only some, it seems.
I was at the Perth double-header a couple of weekends ago, and of Wales, Ireland, England, and France, on the English jersey was being sold. There were supporter gear for the other three nations taking place (double chevron flags, the equivalent t-shirts, hats (I think), ect) as well as generic RLWC 2017 gear, but alas, only English jerseys. Through all the looking around online that I've done in recent weeks, it seems there are only a few nations who have their jerseys for sale in Australia: Australia (obviously!), New Zealand, England, Ireland, Tonga (?), Samoa (?), and perhaps Fiji.
It's a shame, because I really think all the jerseys this time around look brilliant and I'm sure they'd sell a heap of all of them if they were readily available.
Yeah, at the games!!
I would imagine in the various sports and online shops too.