Wellness makes grain-free jerky squares (venison, salmon and venison, and a couple of other flavours) that are easy to work with.
You can also use no-grain weiners and dry them out in the microwave. Or boil meat (beef heart is a favourite here), slice it, then bake it for a bit.
I also use beef liver and other treats from N/A Nothing Added (GTer quietstorm). They're crunchy, so they work best with a dog that chews fast.