I can't believe no one has responded yet. I'll give it a go...
I've got something similar to this:
Blazer/Horn (BH103FBL) | AutoZone.com
My bike has the Buell conversion, so I don't have a ton of room for the aftermarket horn. After searching and searching for a spot, I fixed it up this way. Bare with me on the pictures as they aren't the best, but I think you'll get the idea.
From the front/left. The horn sits behind the windscreen but points sideways just above the turn signal. It's attached to a home made bracket that's attached in the channel on the front of the upper triple, where the fork goes through it. This has proven VERY stable and doesn't inhibit the sound of the horn at all. Of course, you probably don't want to be to the left of me if I blow it...lol.
From above. You can see how the bracket the horn's attached to attaches to the front of the top triple. It's held in place by the pinch bolt at the top of the left fork.
This horn is pretty good. It's pretty darn loud too. Although this is the second one I've had on the bike. I learned the hard way not to face the opening of the horn toward forward or it quickly becomes filled with road debris and bugs and causes the horn to stop working.