How do I find my real grandparents?

My dad was adopted. He was born AND raised in Hawaii by his adoptive parents. All I know of his biological parents (aka my biological grandparents) is that his mother was Japanese and father was German and they met in Hawaii during the Pearl Harbor days. I'm 19 and I was wondering if it's possible now that I'm of age to save up money and try to find them. I have no idea how to do this though. I've been to Hawaii numerous times but have never thought of looking for them or asking my dad's adoptive parents about my real grandparents (btw my dad's adoptive parents died 6 years ago so I was also young and didn't think of asking at the time). How do I go about this?