Use the resources below to find trails and locals to ride with.
Most of Hawaii's trails are on Trailforks and we recommend using that. Download the app on your phone and you can use it to navigate while you are riding. It works fantastic when riding unfamiliar trails.
Click here to visit the Hawaii Region at Trailforks.com: Trailforks Hawaii
They are hiding on Social Media. If you have a Facebook account join the 'We Go Ride' group for Oahu or the 'Big Island Mountain Biking' group for Big Island. It's full of locals connecting to ride. I'm usually up for a ride, you can find me on Instagram @mtbhawaii
The other option is to join a local group ride. There are rides Wednesday evenings at Ohana Trail and Saturday mornings at Pupukea trail on Oahu. You can find out more about the rides in the 'We Go Ride' FB group.
Each island has at least one shop that rents. Google is your friend. Or ask around in the Facebook groups linked above.
Bringing your own bike is not always possible but if you'll have a chance to ride multiple days, that is what I recommend.