Gordon, here are the elements:
1. It is a complaint in a letter to a friend.
2. The point is, "I can't get paper. There is a shortage. A lot of paper is being used by the war effort."
3. The "fronts" are the physical theatres of war. It may or may not have been true that the paper was consumed by frontline soldiers, but the point is that the war had made resources scarce.
4. Continuing this vein of complaint and perhaps slightly dramatic exaggeration (as is usual when one is writing to a friend or lover), the "not enough paper" may or may not have been literal. The point is, "I can't get paper, and the shops don't post notices on their doors or shop windows that they have run out of paper. So I have to waste time to go in and ask, only to be disappointed. How frustrating and annoying!"
5. In reality, stationers' couldn't be expected to post a long list on the door on items they were short of in times of war. So the point is to express annoyance and frustration, and not whether the stationers had that one piece of paper to write a notice on.
So in reading your novel, you need to think about life and history as well. That is why a balanced liberal arts syllabus is so important even in high school. I understand that is something that teachers and parents in your country are not yet convinced of. Your schools are basically exam crammers.