INDIANAPOLIS ??? Standing in a small booth surrounded by displays for rifles, pistols, holsters and other firearm accouterments, the Rev. Kenn Blanchard signed copies of his book ???Black Man With a Gun: Reloaded.??? Amid the sea of thousands of white faces that descended on this city for the National Rifle Association convention in late April, Mr. Blanchard, an N.R.A. member since 1991, offered h