I talked to Jack today and he said that Bruddah Smitty (previously of the Sons of Hawai'i) does a jam up in Waimea at the Paniolo Cafe, 1st Sunday of the month from 3pm till 6pm. I'm not sure what the setup is. It sounds like it's more of a performance that you can join in than a song circle.
Do you know of any music related stuffs in Honoka'a? We are staying with friends in Kona now, but I think we will end up there.
Edit: I now see that you are in Hilo. Long drive to Kona, but I love it over there. What kind of jams, etc happen there? Honoka'a splits the difference.