Hi CNJ,
Dreamfoam (Brooklyn Bedding) only sells these mattresses online through Amazon so they wouldn’t be available anywhere else.
Having said that … you could find mattresses that had a similar construction (a good quality polyfoam base with several inches of latex in the comfort layer with a quilted cover) in most areas of the country including Washington, DC.
Some of the better options and possibilities in the DC area are in post #2 here and if you wanted to test this type of mattress I would call them and ask if they carry a “latex polyfoam hybrid” that has 3" of latex over a high quality polyfoam support core. While this may not be the same as the Ultimate Dreams (latex and polyfoam both come in a wide range of firmness levels and there are also different types of both materials) … it would at least give you a reference point for this type of mattress and if the place where you were testing it was also able to provide you with the firmness of each layer for a mattress that you liked then this could also be helpful in making a firmness selection for an online purchase that used similar layers.
Chuck is also quite good at helping his customers make their firmness selections (especially if you have done some local testing) and of course if you do decide to go in this direction also make sure you let them know you are a forum member here so they will include their free shredded latex pillow 
Phoenix