Oxford shows that "look you," "look ye," and "look thou" were all quite current between the fifteenth and seventeenth centuries, with some continued use into the nineteenth. It wasn't restricted to Wales. "Look ye" is the only survival, and Oxford deems it "regional" or "archaic," which means you'll rarely hear it. "Look ye" is limited to "Welsh English, esp. in stereotypical representations."
OTOH, the reduced form "Looky (here)!" still survives in the U.S., but mainly as a huckster's or carnival barker's expression.
Just now I heard an advertising jingle that goes,
"Looky, looky, looky! Here comes Cookie! Cook's Pest Control!"