#1. "RE: L Bracket for 3100?" | In response to Reply # 0
Neither RRS 1(888)777-5557 www.reallyrightstuff.com or Kirk 1(800)626-5704 www.kirkphoto.com list an L-Bracket for the D3100 though they are available for the D3200 and D5100.
I would recommend giving them a call.
Good Luck and Enjoy your Nikons!
#2. "RE: L Bracket for 3100?" | In response to Reply # 0
If you can't find a custom plate for your D3100 you can always get a generic plate, like the Wimberly P-5. http://www.tripodhead.com/products/camera-body-main.cfm
I have two of these plates I use on different bodies. There is one thing about the P-5 that I don't like. It's the gripping surface which digs into the camera rubber base plate. While it certainly prevents any movement between the plate and the camera base it leaves a lasting impression on the camera base. So what i do when I use the plate is cut out a thin cardboard spacer which protects the camera. I use a cardboard thickness like what you would see from a cereal box.
edit: I just checked the features of some of the Vanguard tripods. Does yours accept Arca Swiss plates? The plates we mention are for Arca Swiss quick release heads. If not you can also buy the little adapters which accept Arca plates.
Visit my Nikonians gallery.