If you wanna see the update in MAS, you can just put this code is terminal:
Code:
sudo softwareupdate --set-catalog https://swscan.apple.com/content/catalogs/others/index-10.10seed-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog.gz
press enter, enter you password.
then you should be able to find the update in MAS.