8 Bit Decoder& Encoder for RF 433/434Mhz Rx-Tx

hello folks. I want to use a 433Mhz RF Rx-Tx with 8 bit encoder/decoder - HT640/HT648L, I'm from bangalore, and i called some of the electronics dealers shops. they said that IC's HT640/HT648L are discontinued. Is it really possible to get these IC's and wat will be its cost?

how can i interface two 4 bit HT12D decoder to achieve functionality of HT648?