The reason they are hard to find is that they really don't make them for rivers. River beds can change very quickly, new sand bars, dry years can drop a river by the tens of feet, wet flooding years, holes can move down river or be filled in, in only a couple of years. Our northern rocky rivers tend to be more "stable" but are usually so shallow they are not considered navagational, thus why make a map. Smaller rivers, or very upstream rivers, you can just about forget it. The army corp of eng will keep navigational maps and set bouys based on the ever changing river bed. So your best bet is to bark up their tree. Best of luck, keep us posted.