See if they are listed on eatwild.com.
When you visit the farm, ask the farmer if he/she will give you a tour. I had a farmer drive me all over his property and explain hundreds of fascinating details about what farming entails (he retired from electronical engineering to take up cattle farming, so he was very thorough). There was a lot more pasture land than first met the eye - a lot of times, pasture land occupies land that can't be used for raising other crops due to terrain, so it can twist and wind over hills. If you see cattle eating grain or bags of grain feed in the barn, you'll know the farmer is either cheating or grain-finishing (which, nutritionally speaking, is cheating anyway).
You might check to see if your state has a sustainable farming association (we have one in PA). They might be able to tell you if the farmer raises on pasture.
I may be wrong, but the only kind of grass I can recall that is now GMO is alfalfa. And none of the grass farmers (what the farmers who raise cattle on grass sometimes call themselves) use it. In fact, when you visit the farm, ask what kinds of grass he plants -- my farmer used a half dozen different varieties, each with its own reason for being in the mix. Ask if he uses managed intensive grazing (rotating paddocks). Ask what the cows eat in winter.
A way a lone a last a loved a long the ... riverrun, past Eve and Adam's ...