Transmission of bonds

There are bonds of  State Bank of India (Floating Interest Rate Bond in form of Promissory Note ) , Date of Allotment was 24^th January 1994 and Date of Redemption was 9^th January 2004, these bonds were not redeemed at that time, and the holder of these bonds is no more, now we want transmision of these bonds in name of her son's. But no where on website of SBI  these bonds are available so that we can know its NAV. and where to give request for the tranmission as RTA is also unknown to us.