Ronan, Victoria is probably better to answer this, but I believe in the 2.' Beta, you get to the missing files collection by right-clicking on a folder in Library module, and selecting "Synchronize Folder ...." from the context menu. One of the options in the resulting dialog, is "Show Missing Files"
I haven't tested it, because I don't currently have any missing files, and I haven't take the time to create a test catalog to hide some files from.
You're correct, in 1.X, there was an automatic collection for missing files. Rumor is that was removed for performance reasons.