Doing searches, be sure to try the variant spellings Okanogan, Okanagon, etc. Settler-folk usage vs. First-Nations usage, and north of border vs. south of border, preferences vary, but you may find something under a spelling you hadn't thought of. I'm inclined to bet there's something Okanaganian in Linda Allen's Washington Songs and Lore which your local library probably has if you're in Washington State (and if not, they can likely get it anywhere in North America through Interlibrary Loan).

Haruo