I use Reisse Maps for planning all my trips and find them excellent. Very detailed and hard wearing as theye are continually being folded and put in the map pocket of my tank bag when over there. AAA maps are pretty good as well and you will be able to find what you need on either of them.
They are available easily enough on line but I'm lucky enough to have this fantastic map shop on my doorstep and they do
http://www.themapshop.co.uk mail order. For map nerds like me it's a porn shop
If you want more details, you are better off waiting until you get there and buying at any gas station as most of them have good one available for just a few dollars.