I've found a website with actual photographs of specimens (and reconstructions) of the Hallstatt tartan and others here.

For some historical perspective, Hallstatt, in modern times, is a village by a mountain lake in Austria. Near the village is the world's oldest salt mine, and during the early Iron Age the area was a center of wealth, trade, and influence. What is known as the Hallstatt culture flourished in the area of central Europe around 800 BC to 500 BC. Hallstatt culture is believed to be largely Celtic in nature, with some Illyrian influence in the east. It is believed to be from this area that Celtic language and culture spread across much of western Europe, as well as into Galatia (central Turkey). Note that, during the time period in question, the Germanic tribes were confined to Scandinavia and the North Sea coast west and east of the Jutland Peninsula. It wasn't until about the same time as the Anglo-Saxons were flooding into the British Isles that other Germanic peoples (the Bavarians) began pushing into what is now Austria.

I quite like the Styrian tartan, particularly the lighter version, but I would like to see evidence that it, like the Hallstatt tartan(s), comes from an actual artifact rather than, say, Thomas Rettl's imagination.