Adobe removed their downloads of old AIR SDK versions, except for AIR SDK 32.0. They don't have a webpage for it, but there are working direct download URLs that I saved in a Gist here:
https://gist.github.com/joshtynjala/76e80fa8422cdc147733f485b97ae60e
It's very likely that you will be able to use AIR SDK 32.0 instead of 24.0 without any changes to your code. With each AIR update, they mostly added new features and avoided breaking backwards compatibility.
If you run into compatibility issues, though, it may help to use the http://ns.adobe.com/air/application/24.0 namespace in your AIR application XML and set the swf-version compiler option to 35 which is the appropriate value for AIR 24. In the uncommon cases where Adobe changed how AIR behaved in a newer update, they often kept backwards compatibility when loading a SWF that was compiled with an older swf-version value.