The web is great but limited in a lot of ways, go down to Barnes and Nobel’s or some other big book store, look in the military history section you should find books on uniforms. or even go to a hobby store that sells military models. they usually carry these small books that give descriptions and photos of the equipment and uniforms used.

Heck even go down to a army surplus store, a lot of them carry old equipment and some even sell militaria that goes back to the various wars.

If your interested in a Field phone I know a place here in the bay area that has one.

Best of luck and good hunting.