The most reliable source for downloadable PDF material is the official NPTEL archive. For most of his courses, including and Selected Topics in Mathematical Physics , NPTEL provides:
V. Balakrishnan's "Mathematical Physics" is a popular textbook that provides a comprehensive introduction to the mathematical methods used in physics. The book covers topics such as vector calculus, differential equations, group theory, and more, with an emphasis on their applications in physics. v balakrishnan mathematical physics pdf