What earth alarms are there for a 50V System?
That there is nothing available on the market would have been of no concern whatsoever to those writing the standard, unless they wrote it knowing that the lack of availability would make compliance impossible.
Maybe the market will eventually provide something, but since (as usual) this ridiculous requirement will probably be unique to Australia, the only options will be expensive low volume units like the one you posted from AERL.
The reality of all this is that the most dodgy and dangerous DIYers will continue unabated, while those who wish to make an attempt to comply will either do so at great expense, or pay forget about DIYing anything and pay a professional, also at great expense, or throw their hands up in despair and not bother with it at all.
And thats the way we like it in Australia. You shouldn't be trying to learn anything for yourself. You should come home from work and sit on the couch and watch cricket or home and away. We don't want people learning or doing things for themselves.