There are plenty of products that can flush mount, similar to what Teetertotter mentioned, but installing them in the floor in the first place sounds really odd. What was the reason for that?
Here is another example one:
Arlington TVBU505-1 Recessed TV Box Wall Plate Kit Paintable 2-Gang, White - Television Mounts - Amazon.com
www.amazon.com
Standard recessed gang box, into which you would install plates with the binding posts.