Yes, both are exclusively grass-fed. I live in an area with lots of organic farms, so I was able to find the beef fairly easily by asking around. There are also signs up at our local organic food co-op for grass-fed beef. The Weston Price Foundation keeps track of such farms, I believe, and they have a website. It was a little more expensive than regular beef by the pound, but we invested in a freezer and got a whole side of beef, which ended up being less expensive per pound than conventional!
The best part of that was that I got to see the whole farm, meet the animals, and see what beautiful grass they had to graze on. He explained his system, based on New Zealand's way of grazing animals, rotating them every three days through each of ten pastures. It was a beautiful place, and the animals seemed very healthy and content.
Bison has been a little harder to find at a low price, but it's SO tasty. We've found one person who will sell it at a small discount and deliver it, but we're not ready to commit to that quite yet. A few other families may be willing to go in on it with us, though right now, since my meat cravings have subsided so significantly, I'm having second thoughts about that.
Mercola sells bison and I think beef online, as you probably found out, but it's quite expensive.
When we lived in the Chicago area, there were groups of people who found creative ways to get raw milk, grass-fed beef, organic veggies, etc. for much less than going to whole foods. They would get Community Supported Agriculture (CSA) subscriptions for the vegetables, and one person each week would drive out to a farm where they cooperatively owned a cow to get raw milk for everyone, and they'd pick up meat while they were there, too. It can be done, but it can be a lot of effort to find or form the groups. I'd guess that the local natural foods store (preferably a co-op) would be the best place to start. Online would probably be the most expensive option, but it's nice that it's there for those who can't connect with such sources!
Hope that helps. Someday, the prices will come down because everyone will understand the need for this and farmers will return to nature! (I hope!)