Here's an odd item:

http://www.ebay.com/itm/GE-LUCALOX-SERIES-150W-HPS-6-6A-BALLAST-85299-/231089309552?pt=LH_DefaultDomain_0&hash=item35cdff0770

It's a ballast for a 6.6A series street light circuit for HPS lamps.  Note the thickly insulated primary wires for withstanding the several kV of the series circuit.  I guess a few municipalities that still use a series system have HPS fixtures.  It looks like a transformer with the right ratio to deliver the proper lamp current with a user-supplied ignitor.  Definitely a niche item. 

Still interested in seeing a "unicorn" 6.6A ballast for HO/VHO/PG fluorescent street lights.  I guess it would be a transformer with extra secondary low voltage windings for the filaments (or just a transformer for a preheat fixture).