I ran across this County page that has shoreline maps for each district, and a listing of public access points for each map, going all around the island.
For each point of access, they explain the road conditions, parking walking involved, facilities if any, really useful information.
Another useful aspect is you get a very good outline of the shape of the coastal bays and points. You can see them on Google Maps too, but this is just the hard outline, so it really brings the coastline into focus.
One thing I noticed is they say a lot of places have hazardous waves and footing, including some that really don't most of the time.
I would just check some other beach sites for the scoop on the beach. Google Big Island Beaches and you'll get good sites. I think the County is being very conservative, probably with its liability in mind.
Note: The map itself isn't clickable. You want to click on the district names in blue above the map. The link to "important information" above the districts has a lot of good stuff you should read if you are visiting. Enjoy!Edited: 26 January 2013, 08:09