Hello Ralph.
I’ve just shot a promo on the C300 and initially encountered the same problem as you. We shot abroad and ‘guerilla’, so didn’t have the CF/disk images cards to import directly to the FCP plugin, and I can’t remember the exact file path ro recreate the disk image.
The only work around I can think of, for now, is to encode with Adobe Media Encoder. This (for me at least) is the only application that can read .mxf files (after trying MPEG Streamclip, Episode Pro and Compressor).
So, I drag each .mxf file into the encoder (it won’t read the files if you try and batch drop the folders in), and then batch select them to export to ProRes. Depending on how many files you have, this could be a long process. My first card contains 54 folders, from which I was able to drop the individual files into Media Endoder in roughly 5 minutes, and have everything transcoding soon after. So, actually, it’s not quite as painstaking as I originally imagined.
I hope that helps!
Tom