I think using the key for a HD weapon is not a great idea. Or a trigger lock or a padlock, or anything else that hinders you from using the gun. I also don't advocate leaving it out for intruders or children to get it. Instead of getting a replacement key, I would recommend you get a quick access handgun safe like sentry or gunvault. No key, 2 second access. What isn't there to like?
If you have kids, go to corneredcat.com and read about guns and kids.