I believe that APP-6(A) is the source document (under STANAG 2019). APP-6 has recently been rewritten which is the one that standardises terminology and is on the intranet. I cant find APP-6 (A) on the intranet, but try the wikipedia entry for APP-6a, this has a link to a draft PDF document.
As QRK says there is a UK guide in the battlebox that is useful, but this will not be definitive if you are working in a NATO context.
You might find a use for current NATO map symbols as a microsoft compatible Tru Type Font, courtesy of my old comrade in arms, Maj Tom Mouat MBE of t'Really Large Corps. You may never need a Rotring stencil again.