We all know REI is an uber-ripoff and their markup is almost criminal, but they are the only ones I know of where you can not only buy topo maps, but peruse them before you buy. They have a big map table, with your state under glass in the tabletop, and it's marked off in quadrants so as to help you find the exact area you're looking for.
Keep in mind that there are several different levels of detail: 1:50,000, 1:25,000, and so on. The higher the detail, the less area that is covered. I prefer better detail, because A) I used them solely for backpacking and I did not transit a big area very fast, and
B) The better detail helped me ID landmarks and topographical characteristics more easily, and that's a big stress reducer when I'm in a new, unknown area and far from my car.
Your goal of buying them for the entire contiguous US will cost you several thousand dollars, I think.
Competence in reading topo maps has saved my bacon more than once, and lack of competence has put me in hot water more than once!
Make sure you have a topo map of your area, scaled down enough so you can see gasoline/diesel/jet fuel pipelines are going thru your area, And Where The Pumping and or Pressure Relief stations are (Should you ever need to take a sample for quality control of course)Look at the USGS website, www.store.usgs.gov/, and see what they offer. Also try Wide World of Maps, www.maps4u.com, and My Topo at www.mytopo.com.
I have some large scale topos of some states I got years ago. As has been mentioned, they give a vague idea of what's there, but are too large a scale to really be useful. A better thing, but not very portable, would be one of the raised relief maps of your state, or the US if you really want one.