Xcode for Snow Leopard: where to get

Visit Apple's Xcode page.

Once you click "View Downloads" and log in, you should have access to previous versions of Xcode.

If you pay the annual fee to Apple for iOS Developer access, you can download Xcode 4.2 (and iOS SDK 5) for Snow Leopard directly from Apple. Otherwise, you can either torrent it or, with free registration, download the older Xcode 3.2.6 (and iOS SDK 4.3) for Snow Leopard directly from Apple.

Source: http://iphonesdkdev.blogspot.com/2010/04/old-versions-of-iphone-sdk.html

None of the above suggestions worked as of July 2018, though the following link (developer access required) should do the trick for OS X 10.6.8 (using the v1.1 updater from Software Update): https://download.developer.apple.com/Developer_Tools/xcode_3.2.2_developer_tools_beta_20728/xcode322_2148_developerdvd.dmg