Hi T,
I have never heard of it, but the web has plenty of info on this supplement.
Here is their email: ***@****--maybe they can tell you where they distribute in India--or you can order it direct from them.
CML
this is a herbal supplement and most Vets carry it or can order it for you. I couldn't find Rehmannia 8 but I did find a supplier for Rehmannia 6( I think that means it just contains 2 less strains of bacteria??) you can check to see if this place ships internationally, many do.
good luck....p.s beware of so called 'pet' herbs many are not safe for cats.
http://www.onlynaturalpet.com/products/Vetri-Science-Renal-Essentials-Cat-Supplement/125043.aspx