How to Save & Load the default ZBrush
Reflection / Environment Maps, and where are they located?
Default maps are in the ZData directory, which should never be modified in any way. In the case of materials, they are not typically going to be found anywhere in the ZData folder due to the fact that they are a part of the material file itself. In other words, they’re saved into the .ZMT file rather than being a separate image that the material is calling. Therefore you will not be able to extract those maps from ZBrush for use in other materials or places.
You can edit any material to use a different map, though. Simply load the desired map into the Texture palette, open the material that you wish to modify and click on the thumbnail of the current map. This will let you select your new map, which will immediately update the material.
Very informative, thank you. 
What I was really wanting to do was make a copy of the map to modify a bit, and did not want to F-up the original Material the map was contained in.
I suppose a screen grab of the map would work.
When creating Maps of this type, what is the best size to use Enviro / Reflection Maps?
(512 x 512?)