The time period of 490 and 375 BC covers the Greco-Persian Wars, from 499 to 449 BC, and the The Peloponnesian War (431–404 BC), most importantly through the reign of Philip II of Macedon (382–336 BC), father of Alexander the Great.
The Greeks and the Phoenicians were the two big trading peoples in the Mediterranean. The Phoenicians had been conquered by Cyrus the Great in 539 BC, and mostly controlled the southern Mediterranean. In competition with them, the Greeks had established settlements as far west as southern France and Spain, Celtic territory, which went all the way to Scotland.
The Greeks did lose control of these settlements to the Spartans, but at some point, if this steel was imported into Scotland, it could have had half a dozen possible points of origin. Since steel is so much stronger than iron, it would have been of great value.