Well first off, welcome to the Benelli forums!!!! I hope you enjoy your time here and learn as much as I have from all the great guys on here. I'm glad the list of companies has helped you, I am currently working on something that will be a type of FAQ so new people can reference when finding parts and companies for the Benelli shotguns, still needs more work and want to clear it with the other mods first.
As far as two point slings go, there are a couple threads of guys posting all their recommendations if you want to see more, just look it up in the search. My personal favorite for the shotgun is the Larry Vickers Blue Force Gear non padded. That is my personal choice and what I train with and I love it. Others will have their favorites. My suggestion is if you can go down to the store and check them all out and see what you like the most. Hope this info helps!