It’s been confirmed that the previously retailer-exclusive classic costumes will become available June 7th on PlayStation Store and Xbox Live Marketplace for $4.99 and 400 Microsoft Points respectively, here’s the trailer with some gameplay footage:

This pack includes 7 klassic kostumes and 3 fatalities, you can check how to perform these fatalities in the Finishers page, look for the 3rd fatalities for Scorpion, Reptile and Sub-Zero.