All kinds of Nicaraguan maps.
This map will help you figure out where the regions are. Another "almost free" map, the best I have seen, is here. [Thanks Julie.] Finally, the Perry-Castenada map collection at the University of Texas has some really nice maps.
The Nicaraguan government has quite a few maps available INETER . The only downside is that they are not PDFs so they don't scale. But there are maps there I have not seen available on-line elsewhere.
Carl just pointed out another map of Nicaragua as a PDF (meaning you can zoom in). It was done by the UN and, as far as I know, is free to use. It is uploaded here .
Here are good road maps from the government of Nicaragua.
If this isn't enough for you, we also have the NicaLiving Map Gallery.