You just cut the center from the outer casing.
Then re chrome both
And last weld them back together. There are steel inserts in the aluminum center that you weld to. This is a common deal.
I searched for couple of years somebody locally who wants to make that and nobody wanted... The ones I had were also 6" and wanted to go 7" so just changing the outer ring from any stock steel donor. They were Keystones.
Need to note, that could have being cheaper than buy and ship overseas, that's the reason to find soomebody locally to modify the ones I found used down here. I finally gave up.