Original WW2 military intelligence documents and other book-collecting opportunities1. UniqueOrRare.com : A changing selection of original WW2 military planning and intelligence material. Most of these items appear for sale so infrequently that you could search for years without coming across another.
2. Coloptics.com : Digital re-issues for collecting or display of old, rare and unusual UK WW2 and other local history photographs you're unlikely to come across elsewhere.
3. @UKBookInfo on Twitter : Worth noting, maybe - occasional pointers to (mainly) booktrade-related happenings, people and events, and interesting or unusual old books for sale.