License Plate Fastener

My 2016 550 Special lost the hardware that was holding the license plate bracket to the body. There was a #10-24 screw in a black threaded rubber plug. It had some electrical tape wrapped around it, apparently to keep it anchored.

Can anyone help with what the proper fastener is, I tried to find something in the fasteners drawers at Home Depot but for 10-24, the options were square clips that don’t fit into the round, appropriately 1/2” hole.

Embarrassed to ask this next question - how does one retrieve nuts that drop into the hole and down inside the body? I haven’t removed the second screw on the license plate frame to see what the nut there looks like for fear of losing it.
Thanks in advance.

 

My 2013 just has sheet metal screws holding the bracket/light on. The ½ inch hole merely lets the wires in. (I’ve taken the assembly off several times). The rounded aluminium creates a trap for something dropped in this area. A fiber optic viewer and a flexible grabber is the only thing I can think of for retrieving something.

 

Thanks. What I have is three holes where wires go through the center one and the left and right holes are about 1/2” ID.
The screws on mine are #10-24 machine screws. I’ve seen some threaded nylon grommets on Amazon but they are 1/4”.
Thanks for the tip about retrieval. I didn’t want to miss some easier means to get stuff out of that soace.