Fill a case with 12 flavors of product

[Fischer124]

I have a shipping case that needs to be filled in the cart with 12 bags of candy.

 

I want the customer to tell me the number and flavors they want. Exactly 12 bags in a case.

 

 

For instance one Brand has 21 flavors and I want the customer to indicate which flavors they want and if they want more than one of any flavors.

 

I need for the customer to tell me something like this:

 

3 bags of cherry, 4 bags of chocolate, 5 bags of grape.

 

 

I might want to keep it to one brand or add other brands to the case. How can I add a set of choices, say a quantity button next to a flavor. Then have it max out and stop the customer from adding more than 12 items to the case?