Hi rsterl,
I used a starting point of West Chester and these are the better choices I know about within a range of 50 miles …
http://www.magicsleeper.net/ and http://www.mattressandfurniturestore.com/ Pottstown (or Pottsdown), PA. Local factory direct manufacturer that makes a range of good quality and value mattresses including two sided innerspring mattresses and a number of latex and latex hybrid options. Family owned and good people. They also make custom designs and sizes and and they are also a member of this site.
http://www.verlo.com/ West Chester, Broomall. Regional factory direct manufacturer. Makes a range of memory foam (including gel), latex, and innerspring mattresses. There is a wide range of choices here. See post #17 here for some feedback about the West Chester outlet.
http://www.croydonmattress.com/ Bensalum. Local factory direct manufacturer. They also make mattresses using a range of materials but the value here is not quite in the same range as other local manufacturers. I also had some difficulty getting answers to my more specific questions and he is not as focused on materials and tends to generalities more than most most factory directs.
http://www.yourorganicbedroom.com Doylestown, Paoli. Retail sleep shop that carries OMI, WJ Southard, Naturepedic, Savvy Rest, SleepTek, White Lotus, and Suite Sleep mattresses. These are all high quality mattresses and would make a good place to test various latex layerings but they have a more “organic” focus which also translates into prices being higher than similar products made by local manufacturers.
Phoenix
A larger list centered on Philadelphia/Wilmington/Trenton is in post #4 here