FYI - the 'beef' burgers that you see on the menu's in Mumbai restaurants (Indigo, Leopold, even Hard Rock) are all 'buffalo' burgers, not cow -- which in my opinion makes a BIG difference. They are no where as juicy and flavorful as their counterparts outside India.
It's still illegal to slaughter cows in most of India, so you wont find the meat in any of the hotel restaurants either. The only place you might find cow meat is at Mohd. Ali road during Eid which also is not very easy.