If you really want one,
-Enter game
-Go to sandbox editor
-Open map
-Adjust map to see everything
-hit print screen
-open paint
-paste
-save
-open file put it on second screen
-???
Profit
The above worked for me in with Arma II but the game only is on one monitor not both but I do not have a fully detailed map just a area and can judge where I go.
As for those guys who say "its not how its meant to be played" that statement doesn't really hold up when BI themselves have given and will eventually give Arma III digital copies of the maps to those like me and other who purchased similar deals. TS and Vent and other third party programs also fit in the same cateogry yet very much used along side Arma in various servers.
I haven't played around with a GPS yet but that essentially was a mini map for in game in Arma II.