You could try call or look up "river and trail outfitters" (near Harper's Ferry, WV). I worked for them a million years ago but they're good people and could give you good scoop. I think its too late for the North Branch of the Potomac to be running. There used to be a play wave called WHITE HORSE below the confluence of the Potomac/Shenandoah, near the take out for the daily stretch. Even if there's no big play its a BEAUtiful stretch of river..."blue ridge mountains, shenandoah river....."
"You know that old trees just grow stronger and old rivers grow wilder, everyday..."