Michael At Omega Billiards use to have some, and had some in Las Vegas BCA 8 Ball Event last year. I saw the difference, but the copies were good copies.
The one thing I noticed about the copies is that they are flexible. You can squeeze them and actually compress the tubes. They look the part, but they are not nearly as strong as the real thing.
There are many versions of Whitten knockoff cases. Do you want the ones that look exactly like the real thing from ten feet away or the ones that borrow substantially from the Whitten look?
There are very good ones made with tubes, there are very good ones made with a single tube and soft interiors, there are very bad ones made with both. There are currently three or four sources in Asia to get these cases including one that may or may not be using the Whitten name legally.
There have been a few importers who have brought the copies into the USA. I personally consider it thievery to import or purchase direct copies of cues and cases. But that is another discussion that is endless.
My apologies for not being helpful on this subject. I am certain that someone will provide you the useful information you seek. I hope that the reason you cannot find them advertised on the web as available from US based importers is that Whitten is aggressively pursuing their rights and stopping it.
My old Whitten case has been around the world with me and probably inspired some of these knockoff artists.