That should be a sort-option in iPhoto. I mostly use Aperture, but I can sort by filename, date/time, or any of a number of other criteria.
HOWEVER... you should probably switch to something else for handling photos out of a 5D III. iPhoto is designed for working with JPEG images. While it can import RAW... it immediately converts RAW into JPEG and then does everything in JPEG (in which case you lose all the advantages of RAW).
Apple's Aperture is still sold, but Apple has announced that they don't intend to continue to develop it. So I can't recommend that product anymore (it's advantage is that it shares the iPhoto library... so that would have made converting extremely easy).
The most popular product is Adobe Lightroom (I still haven't converted). But if you're using a 5D III and shooting RAW (and for so many types of photography, RAW offers numerous advantages over JPEG) then you might want to consider moving your photos into Lightroom.
Tim Campbell
5D III, 5D IV, 60Da
