Most all of their towers follow a frequency plan. So when a site id 1 changes in one area, all site 1s should change. This allows the radios to work when travelling to different areas and having to keep reprogramming radios statewide every time a site changes. If a Des Moines radio programmed for Site ID 1 travels to Cedar Falls, it'll simply use the numbering plan for Site ID 1 in Cedar Falls. All sites 1-14 should be the same.
The oddballs above 14 are the only ones that have individual licenses.
Finding new towers shouldn't be too hard. Just scan the area 854-860 area, when you hit an EDACS control channel, just check the numbering plan using that frequency. It is more than likely similar to another. If the site is one of those oddballs above 14, it more than likely has a license somewhere.