There should be XDCAM MXF options in the transcode window.
You can also right click on the sequence-->Export to Device-->Sony XDCAM. If you don't have an XD device mounted you have to fool the Avid into exporting to local or connected storage. It wants to see an actual XD disc. Place a folder called 'Clip' and a file called 'mediapro.xml' on the root of the drive you want to export to. If you do this the drive will show up as an option in the Export to Device dialog. Note that you can use a text file or anything else for the XML file; it does not have to be a real XML.