As to your first question that's almost impossible to answer. Obviously large cities would have the most cases on AMW, but as far as small cities (or relatively small cities like Amarillo) that got a surprising amount of cases or connections on the show that would be hard to answer. Maybe the town of Hollywood Florida is the only obvious example since that's where the tragedy that started John Walsh's quest for justice happened in the first place but other than that no small or mid-sized town jumps out at me.
As for Holberg, she was capture #449. All you have to do is look at the capture directory thread and keyword search/find in page to find what number a capture was (all listed on pages 1 or 2):