Unfortunately there are no "legal" copies of the spec that can be downloaded at this time. If you were a SMPTE member you could get access to various draft versions, but again that only comes at a cost!
There is an MXF book coming out in the next few months, it can be found
here
This again will cost, but it would be a good place to start.
Sorry to be of such little help
![Crying or Very sad :cry:](./images/smilies/icon_cry.gif)