Ok, I've hit on something that's at least better than the "squashed dog" sound that currently plays. It's exactly .108 seconds, and while it's not even close to an actual knocker, it will get me by for now.
One caution - you have to set the knocker volume to low. I don't know what happens, but having it on high makes it sound awful. Hell, the one that's in there by default might be so bad on low.
Edit: Ok, for some reason I can't figure out how to attach files. Drag file into box under post, click Insert, right? Anyway, you can just download it from here. https://www.dropbox.com/l/Bf7j7VCBVrZ9MhUEwTfQza