Hi Mike, got your email. The River Fly Guide is just outside of the I-Park/Emart gate of Yongsan Army Base. Just ask anyone on base and they'll know where it is. As you exit the I-Park/Emart gate look to your right and you will see a small parking lot. He's in there; white door with a large window. Usually just tying flies and drinking tea. Take a map of Korea and he'll point out some spots. Make sure to buy some flies from him to reciprocate. I don't know what his rates are but I highly recommend using him for a day. My favorite place was the Nurinchon. Caught many Lenok there. Also, I recommend not going out on Sundays; very bad traffic coming back to Seoul.
Make sure you call him to ensure he's in. mobile : (010)2495-1130