The only Okinawan spear I ran into (on Okinawa) was the nunti, which I believe is a fairly recent invention. The story passed around by the grandmasters I met (Kise Fusei and Shimabukuro Eizo sensei) was that, due to the unavailability of metal on Okinawa (it's a coral reef), metal weapons and armor were unavailable; hence the weapons tended to be descended from farm implements or readily available natural materials.
SPC Jason C. Diederich, MOARNG
FEMAS, Bujinkan Budo Taijutsu, Kali-Silat
www.geocities.com/shaolinninjamarine