If you want to know the percentages you go find them, mate. It's simple math really. An US Naval Academy average graduation class is about 1,000, which starts from a plebe class of 1,300. The class of 2014 was 1,068 graduating midshipmen. Of that number 265 went on to become Marine Corps officers.
I did not say that it never happened that officers came from one branches of service to the navy. I said that it was rare. The present Commandant of the Marine Corps would know it to be the truth. In fact the present Commandant of the Marine Corps did *not* come from the Navy. He came to the Marines via ROTC (you know where the R stands for reserve?), and was commissioned as a second lieutenant in the Marine Corps. That he was a naval aviator is a semantic distinction as the Marine Corps is part of the Navy, and the Navy takes on some Marine Corps pilots. However, General Amos never held the rank of ensign, nor any other naval rank, other than those associated with the Marines, because he was never in the Navy. He's a marine.
The context of this discussion was how one (Sandgoose) might become a reserve officer in the Marine Corps. The answers to this question are varied, but you stormed the beach, telling everyone that's not how it's done. The bottom line is that the Marines get their officers from a variety of sources, and very few of them come from "the Navy". A good number of them come from the US Naval Academy, but that differs entirely from what you suggested.