Best is to get a simcard from there, i do not think they are available here. If you are going for a short duration and have a address there you can always order a sim card from ebay. Order in advance so that by the time you reach there your sim card has been delivered.
ordering from ebay has the hassle that you will not have a sim card on landing in US but it is very cheap.
for example a usual $40 monthly plan can be purchased in $15 from ebay.