Only LMDE would have a Mint meta Xfce package now, as an Ubuntu based Xfce spin no longer exists. However, don't let that stop you. There are still the Ubuntu based packages in the Mint 12 repos, as many of the repos are actually Ubuntu repos. You want to look for xfce and browse the list of packages. You'll find everything you need to have a complete Xfce desktop on Mint 12. A couple of the main packages are xfce4 and xfce-goodies which will bring most of everything with them.
Mint 15 Cinnamon RCHP2000 Notebook, 4GB DDR3, ATI Radeon 6310