What receptacle for 240V 20A in the States?

Your dryer probably runs off of 240. I guess you could get one of those big ol dryer cords and receptacles at Home Depot.

http://www.passandseymour.com/pdf/U029.pdf
will show you HD 240v devices

The power cord you have can be used for 240v because each conductor will be carrying half of what the hot conductor did when you were using the cord for 115v. Change the plug to the appropriate 240v and you're done.

You don't need a dryer cord. Your local hardware store has plugs for 220 volts, used for some large window air conditioners and shop tools. The plug looks just like a 3-prong 110 volt plug except the power prongs are turned 90 degrees.

Wagzel:

Your link leads to some great quality Pass and Seymore outlets but only one model (the 6-20 R) is designed to prevent it being used with a common 120 Volt household plug.

Murphy's law: IF someone can plug into an outlet..... they will.

Sure, the Hoover will vacuum better than ever for a couple of seconds, but the smoke and fire is not worth it.

Eldartford's suggestion is better.

The plug he's referring to cannot be mistaken for a 120 Volt nor will the 120 volt plugs fit the slot.