Two ways:

1) The DOFFCALLS channel is where players call out rare/important assignments. The common acronym for the mission you care about is "NADORC". Important note: this is a very serious "calls only" channel. If you have questions or just wish to chat about DOFFs, the correct sister channel is DOFFJOBS.

2) A few volunteers try to input the various calls into a shared spreadsheet located at http://bit.ly/DOFFS . Once you pick a mirror, the mission you care about should be somewhere on the rightmost column.