Added: On reflection this answer is "off tangent" BUT still does actually address the question asked. It may not answer a more tightly put question. While I anticipate that some people will have fun downvoting it I'll leave it be as it does add to what was asked.
In the example given " ... you was ..." is definitely grammatically incorrect. However there will be exceptions which allow or appear to allow the described construct.
Having said that, now let's think of some examples :-).
The first example below does not aim to convey purposeful back-woods feel, or use usage which is now obsolete. It appears to fit your description. But, arguably, it doesn't.
This appears to do what you describe.
While the subject is a group, it's really talking about them collectovely rather than as individuals.
- "Having had your joint entry declined, the correct action for you was to have filed an appeal using form 397.3.556A"
Here the you is plural. The speaker uses 'Gentlemen' which creates the sense both of a group of Gentlemen and also of people who are gentlemen individually. You could substitute the name of any member of the group for "gentlemen" without other change. He is speaking both to the group as a single entity and also to each member as an individual.
- "Gentlemen, you will recall that what I told you was "Drive safely, preserve nature and always wear a helmet".