It really is a widely used and very effective product. It's certainly not the cheapest, nor easiest to work with, but worth it in the end.
Unless someone from Hawaii responds here, your question regarding where to obtain it may be a project unto itself. There is no shortage of online suppliers, of which may or mat not ship to Hawaii. As others have contributed, there are several retail outlets for it as well.
It can be re-generated and the process is documented in several places on the internet. But probably only makes sense for high volume users.
The real trick to using it is to keeping it in a fine mesh media bag and assuring water flow through it. Though most bags are fine, the cheapest ones will actually have a mesh size that will let some of the grains escape and make a mess. The instructions say a media bag is recommended, but it should really be more emphatic, and Seachem would help their cause by just stuffing a media bag in each container.
If you do use it, you'll be hooked. It doesn't take much to be effective and won't effect water chemistry like carbon.