HCF Controller described a TCAS RA event involving an in bound Air Carrier and an unknown VFR aircraft near UPP VORTAC; the reporter noting an airspace change is need to increase protection for air carriers.

Narrative

I was providing OJT on R5. My trainee was working several approaches to KOA. Aircraft X was descending on the VECKI6 arrival for the ILS to KOA. He was just south of UPP VORTAC. I saw a VFR traffic (which is common and numerous in that area) flying Westbound from MUE to just South of UPP and crossing the final approach course. This has been a hazardous area; since KOA has become so busy with uncontrolled traffic flying without communications with anyone. I was waiting for my trainee to give traffic. When I saw that the developmental was not seeing the traffic and was not going to give the traffic; I told him/her to give a safety alert. The Conflict Alert went off at the same time. The Aircraft X did not see the traffic and we were not talking to the VFR traffic. Aircraft X received a RA and then immediately saw the traffic. Recommendation; we need to change this area around KOA to a Class C airspace. Traffic has become so busy now that it is hazardous to have so much uncontrolled VFR traffic that we are not in communications with getting in the way with the IFR traffic. This happens on a daily basis.