Getting the classic USGS paper quad maps is an almost obsolete now with cooler options to get the maps so I’m not listing the paper map dealers here. You can find them via google though.
The coolest mapping option is mytopo.com. You can get customized maps which can span multiple quads centered precisely where you want. The maps look awesome and are waterproof. We have mytopo options for all state highpoints on our highpoints list!. Mytopo has partnered with topozone and any map there can be bought by clicking on the option (on the lower left of the topozone map).
Maps are also available in the state highpoint guidebooks by Charlie and Diane Winger and Don Holmes. Those maps are not quad level detail but may be all you need particularly for simpler highpoints. If you are hiking a more rigorous highpoint then you should definitely get a full blown topo map. Important Note: Before buying the mytopo map make sure it is centered so that it catches your entire trail. Our map links default to the highpoint center.
Getting full blown USGS topos on a CD can add up quickly. DeLorme Topo USA has digitalized the maps. They don’t look like the USGS maps but they have the same contour info. Delorme maps for the entire country on a CD (multiple discs for the country) or DVD (one disc but your computer must have a dvd- drive — as opposed to a dvd+ drive)
Maptech and Silva have a 50 High Peaks CD package with all 50 states on a CD. You get a compass too.