I'm looking for a book series which mixes UFOs, the Giza pyramids, Area 51, the CIA, and ancient aliens.

Are you perhaps thinking of Chariots of the Gods, by Erich Von Däniken? He followed that with several others in the same vein.

In this case I would distinguish between fiction and novels and say that this one is not a novel.

There are quite a few Stargate novels

Time Life MYSTERIES OF THE UNKNOWN Book Psychic Paranormal: Psychic Powers.

Time life

You can get the books at thrift stores , like Value Village and Goodwill.

A quick picture of what they look like

What you can do to find those kind of books is go on Amazon, because that is part of solving the problem and it should work.

There is another book by Erich Von Daniken called “In Search of Ancient Astronauts” that you might find interesting.