Haha, I'm glad my simple grill block has inspired you.
Those are simply thumb screws with fender washers. They attach to another fender washer and wing nut on the back side. I wanted to keep it a tooless design in case I needed to remove them on the road. I picked them up at the local home improvement store I believe. Any good hardware store should have them too.
Thumb screw:
The screws on the bottom are just a fairly good sized phillips head screw and fender washer. I drilled holes in the bumper cover and let the screw do the tapping work. They hold great.