Bally Coin Door Part Help

[CJBob]

I've added Bally inserts in the center spot of the coin doors and I want to add lights behind these. I bought the correct sockets (shiny and sitting loose in the picture below) but then realized the metal plate that the nut is suppose to go into on the other side of the hole isn't there.

Can anyone help me identify the name of these and where I would find one? (well actually three)

Thanks

2015-08-30_09-03-52 by CJ Bob, on Flickr