Find an imported forklift repair company/Garage and they would sell these to you but they dont come cheap. You can even try calling some company that sells forklifts as they may probabbly sell spares aswell.
Just out of interest, what would you do with a GNB flooded? These are not very cost effective for domestic usage. For home power back up (if that is whats on your mind) an Exide inva tubular battrey is the best option. Thet do a 200Ah battrey as well which would cost you Rs35-40K depending on the model you choose (There are two I think in 200Ah range)
If you know what you are doing and this isint for domestic use then try for GNB flooded Platinum range if you can get them there is nothing like that.
I hope this helps.