Sorry you’re having trouble finding the door sweep, Ryan LB! I recently learned that the brush used on industrial machines is called a strip brush, and is available at McMaster-Carr, Grainger, and other places.
I found yesterday that my dust shoe and brush were pushing my router off of the toolpath. To avoid this, I recommend making sure that your bit extends below the bottom of the brush when milling the deepest cut for your project (I was cutting 15mm deep). This might reduce the effectiveness of the dust shoe somewhat, but it should still work.
The problem is caused by a combination of the stiffness of the bristles, and the size of shoe we’re using (it creates more torsion on the tool and mount). I am currently working on a new design with a smaller footprint, and am also looking to purchase some much softer strip brush (horsehair, probably). Switching to horsehair alone would probably solve the torsion issue, but I also want a smaller footprint so the shoe is not covering up the work as much.
Anyway, the original dust shoe works fine, just keep in mind the things above, and look for a softer sweep when you can.