With new cameras, it can take a while for Adobe to bring out the RAW file handling updates to allow RAW editing. Unfortunately you will have to be patient, as it was said earlier, we can't expect Adobe to have updates for new or yet to be released cameras available instantly. I had to wait a few weeks for the update to let me use my nex5n, in RAW mode, in Lightroom 3. I'll also be in the same boat as you when I finally get my Fujifilm X-Pro1 shortly as it too will not be supported. You could meantime use Canon's supplied software which you will have gotten with the 5D Mk3 — make a duplicate copy of each RAW file and convert to tiff or jpg to work with meantime.
With adobe, you need to have the patience of a saint, look at the problems many are having, myself included, with LR4 as it won't edit photographs in Nik Silver Efecs or other software. Frustrating indeed!