The 1941 Battle of Thermopylae was real. The battle was a rearguard defence by Australian and New Zealand forces (one brigade of each), to win more time for the rest of their forces to be evacuated from Greece. The pass at Thermopylae was defended by the New Zealanders, and the nearby Brallos Pass by the Australians.

It was a quick battle, beginning in the afternoon of 24th April and finishing at about 9.30pm (when the last defenders withdrew). This was no last stand to the death, just a delaying action by a withdrawing army. This is one reason why the fighting at Thermopylae and Brallos gets little attention. Another is that the losing battles often get less attention (although the prominence of the WW1 Gallipoli Campaign in Australian military historical writing and popular consciousness shows that they can sometimes get a lot of attention). Sandwiched between spectacular success against the Italians in Africa and much hard fighting against the Germans (and Italians) in North Africa, the British/Australian/NZ intervention in Greece suffers from being both a sideshow and a failure. It is not surprising to see 7 hours of fighting in that campaign get such scant attention.

Long (1953), the reference on which the Wikipedia entry appears to be based, is available online at https://www.awm.gov.au/collection/RCDIG1070201/ (chapter 6 covers the fighting at Thermopylae and Brallos).

Clark, Chris, Encyclopaedia of Australia's Battles, Allen & Unwin, 2010, lists the battle as "Brallos Pass" and only covers the Australian portion of the battle (which, given the scope of the book, is understandable).