Scows is not ran all the time, if it was then we would all have too many tokens and items (inflation of economy). Scows are announced a day or two prior to the event, but if you become VIP you will know ahead of time by 1 week!
Everyone is wondering what Super Cows are, in short they are:
-5x the normal experience found in Hell Cows (Ncows)
-They are no harder than Ncows
-Same amount of cows as Ncows
-The new unique items can drop during Scows (other bosses can drop them normally)
-This event only lasts for 24-48 hours, you will find out how long once posted
Basically during Scows, you can take a level 1 character and in 9 games make it turn 99 instead of the 45-55 games Ncows takes (B.net takes a whole lot longer than 150+ runs :) ).