Late to the party here... I actually have a similar setup running 2 of the exact same machines. Look for this: NEMA 6-20 outlet and 2 of these NEMA 6-15 to C13 cords Wire this with 2 hots and a ground - don't use the neutral. This will run OK on a 20A breaker.
Looping out to a second receptacle should work fine, if you can't get a double outlet. Worst case, you need wire nuts.
EDIT: One of these should work fine, right? http://www.amazon.com/dp/B0013AK4SE