The wifi antenna connector on the antminer is a SMA FEMALE. The antenna you want will be a SMA MALE. Not a RP-SMA antenna. The antenna you want can usually be found on pci wifi cards or like a foscam webcam. You won't find many US sellers with plain SMA MALE antennas. On ebay, the one you want will most likely have to come from china. I found some at data-alliance.net for $3 but they want $15 shipping.
http://www.data-alliance.net/servlet/-strse-937/Antenna-2.4GHz-5dBi-omni/DetailHere are the cheap ones I ordered off ebay
http://www.ebay.com/itm/320684061024When searching, try using "sma antenna -rp-sma". This will exclude rp-sma antennas from your search.
I found some neat short stubby ones that you could order in bulk for cheap. Not sure why bitmain can't include such a cheap item.
Let me know if anyone finds a cheap supplier that ships from US.