I use a Mesa Boogie 1X12 from the long-head Lonestar head - I use it for a Carr Slant 6V and a Super Champ XD - great match-up to those amps - should work well for your HRD - should be easy to find used if you look in enough places - even new they are not overpriced and are built like brick houses.
I haven't tried one with a combo amp, but the Hermida ported 1 X 12" is terrific. Light, too.