I don’t exactly understand what you want to use pathfinding for. Is it to plan a general route to the target, or to do mid air movements to avoid things trying to shoot it down?
If your just doing flight path, you could use a single graph on a plane and then have “air defense zones” cut a large area out of the graph so your missiles go around them. You would have to do the vertical movement and rotation of the actual missile separately.
For mid air dodging I would use raycasting to detect incoming bullets and move/turn away from them.