I see your point!
The first thing that sprang to Kay's and my minds was: will the Indian authorities let you import your pet boa? Without wanting to cast gloom over proceedings, I can imagine the bureaucracy for that being pretty complicated, though probably not insurmountable with bucketfuls of patience.
I don't have an answer to your direct question about rats bred specifically for pet food. Delhi's a big city and quite cosmopolitan, so there's a fair chance that there will be a supplier somewhere - it's a question of how you track them down. And then how you make sure that they're reputable - the chances are that for every breeder of healthy rats, you'll find several who are a bit less scrupulous.
If you can find someone who already keeps a pet snake large enough to eat rats, then either your problem's solved, or you'll be able to share the burden of tracking down the reputable supplier you need.
Good luck, anyway.