Mostly my wife drives our HRV but I ran an errand in it the other day and I needed the horn...
I was working on our Acura TSX and noticed the horns on it. Took one off and plugged it into the HRV with a ground jumper wire.
The connector is identical, the horn is just much larger and much louder.
A quick cross-reference of Honda p/ns and found that the 2006 TSX horns are also used in the 2000-07 Honda Accords.
Off to a self-serve auto-wrecker, tons of Accords, picked up 2 horns off an '07 Accord, pass and drivers side, high and low frequency.
They look identical to the pics in this thread.
Back home, tested both horns with a 12V test power supply, took about an hour to install both in the HRV, plug and play.
Broke all 3 plastic pin retainers on the passenger side underbody front access panel.
The pin retainers are different than the other underbody pins.
I have tons of various Honda pins, clips, etc. You always need those on hand when working on a Honda.
Replaced those pins and installed both horns. Low frequency on the drivers side and high freq on the pass side.
It likely doesn't matter which side is which anyway.
And now our HRV has real horns for a total of CDN$5/ US$3.75 and a couple hours of quality time in the garage!
Thanks to everyone for the info in this thread...