Its definitely an axolotl morph because it looks like one and no pet store would sell anything other than an axolotl in Australia. Its strictly against the law and no pet store would risk selling an ilegal import so publicly. Sure it happens but thats on a black market, there is no way they would make it into pet stores without them being shut down and the owners serving jail time withing the fisrt week of it being publicly available. No business owner would be that silly. There are very well revised species lists they can and can not sell.
It would be interesting to find out where they were coming from. See how they are produced and supplied. For pure interest i would confront the pet store manager. Say - hello, what type of salamander is that. When they say "Mexicana Salamander", say sorry thats species doesn't exist! And tell them that all salamanders except axolotl are illegal in Australia. Tell they you will report them for selling them... unless of course it is an axolotl morph. If they say finally it is an axolotl or are still unsure, ask them for the supplier, and say you are reporting them unless they can prove its an axolotl or you can contact the supplier to make sure. They should give you the supplier.
I know that sounds horrible... but i would do it. Would be interesting to know who is morphing them, how and why.
And Mexicanum salamander? Sounds like they are covering up the fact they are morphed axies, or they dont really know that much about what they are selling and in that case they shouldn't be selling them at all.