I have an Alienware 15 R2 in which the battery has been worn out. Can somebody please help send a link from where I can buy a battery cause on Amazon India it’s not available right now.

All you can do is search the web for the specific 15 R2 battery part number =
2F3W1 Simplo, 92WHR, 8 cell, Lithium Ion
410GJ Sanyo, 92WHR, 8 cell, Lithium Ion
DELL-Admin