Christoph Golke first reported that cbook.get_sample_data from github is broken:

I have trouble receiving the sample_data from github via cbook.py. There
are frequent HTTP 304 (Not Modified) and 500 (Internal Server Error)
exceptions and redirection to
https://raw.github.com/matplotlib/sample_data/master.

I can confirm this on linux::

msierig@pinchiepie:> python -c "import matplotlib.cbook as cbook; datafile = cbook.get_sample_data('ct.raw', asfileobj=False); print datafile"
Traceback (most recent call last):
File "", line 1, in
File "/home/msierig/dev/lib/python2.7/site-packages/matplotlib/cbook.py", line 688, in get_sample_data
return myserver.get_sample_data(fname, asfileobj=asfileobj)
File "/home/msierig/dev/lib/python2.7/site-packages/matplotlib/cbook.py", line 626, in get_sample_data
raise KeyError(msg)
KeyError: 'file ct.raw not in cache; received HTTP Error 304: Not Modified when trying to retrieve'
msierig@pinchiepie:>