I just happened across this Stumpy Pencil Photoshop Brush the other day. It uses a brush already packaged with Photoshop and applies different Brush Presets to help emulate the look and feel of a blunt pencil. The brush creator is a much better illustrator than I am, make sure to check out the sketches he was able to create using the brush!
If you’re having trouble installing the brush into photoshop, try out the following. The ‘brush’ is not actually a brush, but rather a set of Tool Presets (.tpl), which may cause some confusion when installing.
First, locate your Presets-Tools folder. The path should be similar to the image below. Upload the file to this folder.
Head over to Photoshop and open the Tools window.
And finally Load up the file, grab your brush, and start sketching!