These should be available at any big hardware supplier, like Menards, Home Depot, Lowes, etc. Ask for "simplex receptacles". (You'll need to talk to someone who knows electrical supplies, not the usual teenager clerk.) This is a single outlet, centered, instead of the 2 above each other in a standard duplex receptacle. See http://electrical.hardwarestore.com/14-53-single-recepticles/single-receptacle-601118.aspx for a picture.
But I'm not sure why you would want to use these?
- they cost about 3 times as much as the normal duplex one.
- they take up just as much space as a normal duplex one -- a single gang box.
- but they only provide a single outlet.
Can you explain a bit more about what you are trying to accomplish, and why you want to use these?