Someone posted a link to Alcoa, but Alcoa will not have what you are looking for. Which is probably why you posted, because you already checked all the usual suspects. Alcoa does not make a hub piloted wheel as wide as 6.75", nor as wide as the 7.50" that you'll need to have the correct shoulder support for 265's, with your hub pilot of 170.1mm and bolt circle diameter of 225 mm.
Alcoa does make 19.5 x 6.75 and 19.5 x 7.50, but only in applications where the bolt circle diameter is larger, by 2 more inches (275 mm). There might be a good reason for that.
The same holds true for Accuride. A poster above said something to the effect of "you should be able to find 6.75" aluminum wheels from Accuride as they were available for a Ford Class A chassis." To that I would ask, "Have you driven a Ford motorhome... lately?" Ford does not offer any aluminum wheels on their F53 chassis. Going back for the last 15 years, the F53 wheel availability has always been steel, not aluminum.
The biggest you can go off the shelf are those 29879 Accuride steel F53 wheels at 6.75, in all positions, with a maximum width of 245 tire. That's still a huge, heavy, mileage robbing hunk of tire and wheel. Some of the 245'ss are speed limited to 65 mph. You can find some that are speed limited to 75 mph, but you will not find any that are speed rated to 81 mph as you can with the original 225's.
(I have an F-550 also)