The films were distributed all over the world, so there is some hope that prints could turn up, just as a print of 'Charlie Chan in Paris' surfaced in Prague. These theatrical prints would probably be in a somewhat degraded condition, but film restoration magic can now due wonders with audio and visual improvement.
In addition, keep in mind that the trailer for 'Charlie Chan Carries On' was located in Australia and returned to the U.S. but remains unreleased on DVD. It was shown publicly in Washington DC a few years ago, but I only learned about it afterward. How I would love to get a look at that!
It's possible that some paperwork exists somewhere that describes how many prints of each of these films were struck and to which countries they were sent. That would be a good starting point to try to track down copies.
