I bet the first thing you found was this unhelpful, complex method (surprise!) from Microsoft using tf.exe.
Happily, Clark Sell has an easier way: http://blogs.msdn.com/csell/archive/2006/04/11/573571.aspx
In Tools -> Options -> Source Control -> Visual Studio Team Foundation Server check “Show deleted items in the Source Control Explorer”. Once checked you will be able to use the undelete features from within the IDE rather than tf.exe by right clicking on the item in source control you want to undelete and selecting “Undelete”.
Thanks to Clark Sell for saving me from Microsoft documentation.