Copper was/is abundant and relatively easy to find all over the Bronze Age world. Spain's Rio Tinto region was big, as was Cyprus and Armenia, but there were smaller flourishing sources of copper in Italy, Sicily, southern France, the Balkans, Anatolia, and the Near East.

For tin, in the Late Bronze Age: we have no idea. It a long-standing unknown. The most obvious candidate is southern England, Cornwall and Devon specifically, but England was on the absolute fringe of the ancient world, as regards the Bronze Age of the eastern Mediterranean. Still, Cornwall is a strong contender in the absence of any better explanation. These would not have been direct shipments of tin ingots, of course; instead, the ingots would have passed through several intermediaries before finding their way to the markets of the Mycenaeans, Egyptians, and the Near East.

Another possible contender is the Iberian peninsula, but there are problems. Archaeologically speaking, we don't really have good evidence of tin exploitation there until Roman imperial times, 1200 years after the LBA collapse.

Another possibility, only recently discovered and argued, was the area around modern Afghanistan, via the Persian empire(s). There is as yet no good studies which trace ancient tin objects via their isotopes to this region, however.

Another possibility is the "Ore Mountains" along the border between modern Germany and the Czech Republic. Again, there are problems: very few, if any, ancient artifacts of tin have been traced to this region by their isotopes. Famously, the only object from central Europe in this time period to have been scientifically analyzed (the Nebra Sky disk), has tin with isotopes pointing to Cornwall.

The source would have to be very large. There are tiny deposits here and there in the Med and Europe and the Near East, but none of them would have been sufficient for the amount of tin utilization we see. Some tiny pockets in the north of Italy served the Etruscans in a limited way, but they still had to import more tin. We have detailed records from Classical Athens about how much tin they were importing, and at what prices, but we know essentially nothing about the sourcing of it. Not even Herodotus, who was alive and writing at the time and had a desire to find out the source of tin, was able to find the answer(s).

For what it's worth, most tin sources utilized since the Renaissance are in southern England, SE Asia (Burma, Malaysia, etc), the central Russian steppe, China, and Bolivia in S. America. None of these were likely sources for ancient peoples, except perhaps southern England. While China and the ancient Med. did have contacts, those contacts did not include shipping of commodities on the vast scale which would have been required for the many tin-utilizing industries of antiquity over several thousand years.

Tin sourcing in antiquity remains a debated topic in the archeometallurgical field today. Though it is a bit old now, Muhly's write-up about tin in the American Journal of Archaeology is still pretty good to get an overview (AJA 89.2 1985, pp275-291). Oxford has a monograph Le problème de l'étain a l'origine de la métallurgie (2003) if you want to read some French on the subject. There are some English entries within it. There is also Penhallurick's Tin in Antiquity: its mining and trade throughout the ancient world with particular reference to Cornwall (London: Institute of Metals, 1986).