The main reason 64-bit GTK+ & GTK# aren't shipped on Windows is because there hasn't really been much demand. After all, most apps on 64-bit Windows are 32-bit. Some users did put some effort into fixing bugs, so if you have a compelling reason for needing 64-bit on Windows I suggest poking around in the gtk-sharp-list mailing list archives.
Regarding VirtualMode, I'm not familiar with it but it sounds like implementing a custom GTK TreeModel. GTK TreeView uses a model/view split - so for a list view, one typically connects a ListStore (a simple flat implementation of TreeModel) to a TreeView. Alternatively, you may wish to check Banshee's fully managed GTK# ListView, which was designed for virtualized views onto a Sqlite database.