You did well choosing the SEALs because as you pointed out, a lot of that info is out there. The problem with a lot of elite groups is they run way under the radar, let alone, aren’t acknowledged by the U.S. Government. The easiest to point to is Delta Force, but since the whole Black Hawk Down media fiasco, they’ve really tightened things up. Hell, everyone at Ft. Bragg knows where they’re located but there’s armed guards that will draw down on you should you decide to approach without clearance. The lesser known ones typically operate by “Task Force” and then a number identifier or color and is usually a joint team consisting of all branches (For example: TF123). The most secretive is probably a group code named “Gray Fox.” Good luck trying to find anything on them (although in the book Not a Good Day to Die they’re referenced, but I’m sure have changed names again). To this day the interaction with them was beyond bizarre. I wasn’t even sure they were Americans. All this is out on the net, so I’m not telling anything you can’t find to some degree (nor would I).
Internationally, Mossad is hardcore. I knew some guys who had some insane stories about them. SAS for the British would be a great one to research. French SF wasn’t anything special. We teased them a lot. Personally, I thought the Australian Special Forces and Kiwis were really incredible. Happy hunting! I look forward to your next piece!