The story
None of the various attested forms appear in the OED, in Victor & Dalzell’s Concise New Partridge Dictionary of Slang and Unconventional English, nor in Webster’s New Universal Unabridged Dictionary. According to the RHD, 'looky' (also 'lookee') is an interjection attested from 1875–80 which is an alternative form of the imperative look ye! Similarly, the linguist Andrew L. Sihler indicates that ye, the now-archaic subjective form of the English 2nd pers. plural pronoun, “is fossilized in looky (here) …”.
Etymology from Wiktionary, CC BY-SA 4.0.