Where can I find broadband seismic reflection data?
It depends on what purpose you need the data for. 

This site https://wiki.seg.org/wiki/Open_data gives several sources of data. If it must be land acquisition (as opposed to marine) data then the Poland 2D, Teapot dome 3D, or Stratton 3D surveys might be of interest. 

These free data sets are for pedagogical/research purposes, so if you'd like to 'strike-it-rich' these are not the droids you're looking for.

Hope this helps, 
-D