Missing SAC Headers

[DeCode39]

I downloaded some sac data for the Himalayan region. The network is XF, the channel is *HZ and period is 2002 - 2005. Magnitude range from 5 - 7. The problem is that none of these have the delta, gcarc, distance, baz or az headers. How do I obtain these headers and how do I write them to my sac files?