I have the same problem. It is quirky, fun and aggravating all at the same time. I assume they came in the vents near our windshield washers, since mine are not covered like they should be.
I tried getting the leaves out with Tweezers, but that is not very effective.
What I think is necessary is a vacuum cleaner in the slots where they came in. Tape something over the cabin vents and see if you can suck out the leaves.
