If you're adding to venison, just get a pork shoulder and grind it yourself. You should have about the right amount of fat from the shoulder, if you use it all and not trim off the fat cap. Like I said in another post, I use an extra 10% of fat.
You can buy ground pork and I bet it's trim and pork butt. You can also buy pork trim from a butcher, but why pay for waste? Buy a pork shoulder and be done with it. If you don't use all the ground pork, freeze it for the next time, or make some breakfast sausage.
Todd