I've read a book (Official Secret, Christopher Clayton-Hutton) by a chap who worked for British intelligence during WWII.
He was given the job of providing escape and evasion aids for servicemen, and later, of trying to smuggle such items into PoW camps.
He also had maps printed on silk to give to RAF pilots, and later, had them printed on Mulbery-leaf paper because it is very strong and doesn't rustle if you are pat-searched.
His book describes heaps of other clever gagetry - compasses fitted into buttons, magnifying lenses disguised as the stopper in a bottle, stuff like that.
My favourites were these. When the Germans figured out that the Brits were hiding things in buttons, instead of dropping the idea, he simply reversed the thread of the screw, so that attempting to unscrew the button in the normal direction would simply tighten it. And secondly, they simply magnetised the razor blades being issued to soldiers. Swung from a piece of thread, the end with the capital letter of the maker's name would point north. Simple, subtle, almost free; I love it.
This link
http://www.mapforum.com/04/escape.htm would probably take you to someone who would LOVE to have those maps.
Frankly, I think you could sell them for a lot of money - they are historical curiosities.