Way to rub in your you're in HI >.> lol (I try to visit every few years and my earliest memories are from HI, I always say I'm Hawaiian at heart lol) We are trying to go back next year 
So for the most part unless you feel like importing anything (pretty much all you can do anyways) we get our parts from https://www.k5optimastore.com/ The guys there are pretty good and will work with you. A few of the other guys around the site have used actual Korean dealers for certain things but that can get costly and be custom jobs. There really isn't a whole lot of modding to do with our cars, at least not that is supported in the U.S. our cars are fairly rare here.
Good luck, let us know if you have any questions.
So for the most part unless you feel like importing anything (pretty much all you can do anyways) we get our parts from https://www.k5optimastore.com/ The guys there are pretty good and will work with you. A few of the other guys around the site have used actual Korean dealers for certain things but that can get costly and be custom jobs. There really isn't a whole lot of modding to do with our cars, at least not that is supported in the U.S. our cars are fairly rare here.
Good luck, let us know if you have any questions.