Richard Nelson, the knife salesman who arrived in Point Reyes Station each year as reliably as the summer solstice, died of an apparent heart attack last month while making his annual pilgrimage to West Marin. He was 72 years old. Come May or June, Mr. Nelson would set up shop next to the vacant lot at the corner of B Street and Highway 1, where he parked his Chevy Silverado and an R.V. full of…