As I write this message I am on the phone to Edexcel asking the same thing as you are (I have now been on the phone for 22 minutes and have been passed from pillar to post, following many non-replies of my enquiries in the past few weeks). No-one seems to know exactly when they will be published even though I have pointed out that since many schools run the Science and Additional Science in series (Y10 to Y11), next academic year our year 10s will have completely finished the Science and therefore the IAAs will not be based on last year's work!
Oops, it's now 25 minutes and the outcome is...they will call me back! Aaahhhhhh. Is anyone else frustrated with the admin side of Edexcel?????