Since OV sells a pastured butter as opposed to their regular butter, I don't think all their cows are pastured. Their regular milk products are probably not 100% pastured.
Kerrygold is supposed to be 100% grass fed. You can read about it on their site
. It is highly recommended in the WAPF buying guide.
Natural by Nature, made in PA, is also supposed to be grass fed. It's not as readily available in stores as Kerrygold, but I like it since it's more local.
I don't know of any other brands of grass fed dairy. I get most of my dairy raw from local farm sources.