Installing AC in place of vent

Coleman/Mach 13500 non-ducted. I bought a replacement top unit only to find out my problem was a loose wire. I am now selling the used top unit to a friend. He can buy the lower non-ducted unit of course. He has wiring beside the vent already.

Question is where do we get the metal piece that goes into the vent hole so the top unit can be bolted down?

Does it come with the lower unit, I doubt it and it didn't come with my new top unit. I can't find it anywhere on the web.