If you are looking for history, check John Sells book 'Unante'. Also, Check http://www.karateatucsd.org/home.htm.
As far as training in the style in the U.S., Tomohiro Arashiro Sensei, affectionately known as 'Shihan' to us here in San Diego, would be the appropriate choice based on my understanding of Ryuei-Ryu history. One point of clarification, we are exposed to both tournament modified techniques and traditional techniques. I wish you the best in making this commitment to yourself. Choose wisely and don't look back. Best of luck to you either way.