Here you can find rfid chip as well as Rfid devices. www.atlasrfidstore.com/
For what purpose you are buying this chip.They are of different kind.And are more costly to buy.
RajivConfident ,
am buying this chip for my project , am designing RFID tag antenna and i have chosen Alien higgs 4 and mu center frequency is 915 Mhz . i did not find the chip only in in this website www.atlasrfidstore.com/
Alien itself sells Higgs-4 in two package-types: flip-chip and SOT. The former is more compact, however it requires ACP for bonding. The latter is more friendly for prototyping since it can be soldered. You can contact the Alien sales to buy the chips. But note that there is a MOQ (minimum order quantity) requirement for such purchases, usually on order of thousands at least. You may need to contact some local RFID distributor for chips of a small amount.