Welcome uejru!  
     I did indeed cook & waitress at Chi-chi’s (Shhh!) [:I]   The Suprema sauce was supposed to be a ” Delicious mild green chile & sour cream sauce”   by 1990 it was coming in powdered form that we added sour cream, buttermilk, and freeze-dried chives to and whipped it up into a creamy delight. [;)]  I loved both the Suprema, & the Cancun/seafood sauces as chip dips.  
       Sorry I don’t have an actual recipe but it’s very similar to a green chile-cheese dip only thinned out a bit… Good luck.