Books listed as "on reserve" will eventually be on reserve, but it may take a couple of weeks for this to happen.
Lang also has a 1999 book called "Fundamentals of Differential Geometry", which despite the different title seems to be just the most recent version of "Differential Manifolds". The library has the 1995 version and one or more of the earlier editions, as well as the 1999 book. The library also has a link to an e-book entitled "Introduction to differentiable manifolds", which I have not looked at yet but probably has significant overlap with Lang's other books above.