It seems you're going to have to install under Xcode 5. So go to https://developer.apple.com/downloads/ and log in with your developer ID to get to the older versions. There should be a 4.6.3 that you could potentially download, or even 4.6.2.
Or you could upgrade your OSX to 10.8.
Whichever you prefer.
I can't give you a direct link to it, since you need your developer information to log in yourself. But all the downloads you need are in the link provided above once you log in.