Were the 10 tribes of Israel ever really lost?
The ten tribes of the northern kingdom of Israel are: Asher, Dan, Gad, Issachar, Joseph [2 tribes: Ephraim and Manasseh], Naphtali, Reuben, Simeon, Zebulun.
The two tribes of the southern kingdom of Judah are: Judah and Benjamin.
Note that Levi is not included because they had no set territory but cities of the Levites were scattered throughout the 12 tribes. Also note that many members of the 10 tribes came to Judah when Jeroboam, the first king of the northern kingdom, set up a system of idolatrous worship in order to prevent his citizens from making the pilgrimage to Jerusalem to worship the true God of Israel. That means that by the time that the Kingdoms were destroyed there huge numbers of Israelites living in Benjamin and Judah. Here is one instance recorded in the days of Asa, king of Judah, of just such a migration:
2 Chronicles 15:9 And he gathered all Judah and Benjamin, and the strangers with them out of Ephraim and Manasseh, and out of Simeon: for they fell to him out of Israel in abundance, when they saw that the LORD his God was with him.
Here is a link to a an online map of Israel and Judah with the tribes listed in their geographical locations:
I hope you have found this helpful.