I was about to say, the HR34 is just a power cable, that you can by many places, it is very generic.
If you are using an HR44 that uses an external power supply that DirecTV will send you if your's fails, otherwise you'd be looking at ebay or possibly Solid Signal.
If you are truly looking at the internal HR34 power board, well, used HR34 on ebay would be about the only option, nobody sells those as a replacement part that I've seen.