Hello Harshad,
Elektronika Sales, Chennai (India) are one of the major suppliers of Philips components, try them.
It seems that Philips are continously upgrading their 89C51RD2 series, it will be better for you to adapt to their recent versions, costwise.
89C61X2, 89V51RD2, 89C669 were available with them. I think IAP calls could be common accross the RD2 series.
In the last 6 months I have been experimenting with the 89C51RD2BN, the 89C668 and now the 89C669 mainly due to the supply problem.
You can find an IAP library at ESAcamdemy's web site and probably adapt it.

Regards,
John.