I use this one http://www.tropicaltraditions.com/organic_balsamic_vinegar.htm You might find a lot of balsamic vinegars with "naturally occurring sulfites" because of the grapes. I found this brand at a health food store. It's a super easy dish to make. Please let me know how you like it!
This one is hard for many already "clean eaters" to get used to. Aside from any actual physiological issues that may occur, the bottom line is that stevia is used to either a) make things sweet that shouldn't be sweet or 2) make things sweeter than they are in nature. And, since one of the purposes of the Whole30 program is to reacquaint your taste buds with the flavors of real, whole foods, Stevia doesn't exactly fit the bill.
I hope that clears things up a bit!