Sourcing masa harina (nixtamalized corn flour) on Okinawa main island?

Hello everyone,
Would any one know where do source decently priced masa harina (nixtamalized corn flour) on Okinawa main island? I only saw some at Jimmy's, and it was at premium price.
With all the tex-mex / taco joints on the island, surely there must be a way to source non-overpriced masa harina somewhere?
We'd really like to make our own corn tortillas if possible

Cheers!