You can purchase a map model of any GPS and obtain the maps as needed under accessories.
Try the Magellan
eXplorist XL recreational GPS receiver 98081201 and a Magellan
(Thales) 980611-09 GPS Software - 3D Topo MapSend for USA - 98061109.
You can also do the same for a Garmin
Mapping Handheld GPSMAP 60CSx Waterproof Navigational Device 010-00422-00, or Bushnell
ONIX 200 GPS Handheld Navigation w/ Satellite Imagery Onix200 362000 and get the maps from thier websites.