Have you looked at the one on Mathworks website, in user contributed
files area? If the exact compliance is what you need, it's unlikely
you will find one in matlab because matlab code tend to use 64-bit
floating point while most real-world implementation use 16 or 32 bit
fixed point.

Hi There,
I have been searching for the Matlab code for 40, 32, 24, 16 KBits/s
ADPCM code (G.726) for the last one week but could not find a good
working/ compliant code. Can anyone tell me where to get free version
of the ADPCM code in Matlab 

Thanks,

jagadeesh