I'm looking into this issue too and found a couple of things...
Do you have Xcode installed? And if so, if you do a directory listing of:
Does it include svn? There is an svn in there for my system. I've previously used the "Install Command Line Tools" option in Xcode, so it may have come from there.
But I'm wondering from this, is Apple moving these types of tools to be bundled with Xcode rather than defaulting to available on general user systems?
The other interesting thing about these items being located here, is in the "Preferences -> Downloads -> Components" help notice for the Command Line Tools is the following:
Before installing, note that from within Terminal you can use the XCRUN tool to launch compilers and other tools embedded within the Xcode application. Use the XCODE-SELECT tool to define which version of Xcode is active. Type "man xcrun" from within Terminal to find out more.
Downloading this package will install copies of the core command line tools and system headers into system folders, including the LLVM compiler, linker, and build tools.
Going to the terminal and typing:
Will run the svn that is contained within the Xcode area. I've seen other people add the Xcode /.../usr/lib folder to their path so they can call the commands directly from anywhere normally, and others installing new copies via homebrew, macports or direct install.
The whole situation is a bit confusing really.
Ok, so even though I'd installed the command line tools with Lion and Xcode 4.3, after installing Mountain Lion and Xcode 4.4, I had to reinstall the command line tools to get them functioning again.
So Will is right on the money, with needing to download and run the command line tools