It can be difficult to find the bike part you need when you need it. Here are some places you can get bicycle parts on the big island.

All Kine Bicycles

21st Ave and Paradise Drive, Hawaiian Paradise Park. New and used bicycles and parts.

Ace Hardware Kea'au

You can get bicycle inner tubes and bike pumps here. When I went on 2016-11-25, the largest tubes they had were 26" and I needed a 27.5" tube.

Orchidland General Store

There is a pretty good bicycle section with a decent assortment of tube sizes, bike pumps, and accessories such as helmets and locks.

Walmart

Well, they have bicycle things here too in the back. New bikes for cheap but not the best quality, bike tires, locks, tubes of many sizes (if they are in stock), helmets, racks.