Are you a member of Ravelry? There are TONS of Beatrix Potter/Alan Dart patterns there.
What I have done in the past, with patterns that are out of print, is to find someone on Ravelry who has knitted the item and then sent them a message asking if they were interested in sharing or selling the pattern.
I have traded skeins of yarn for patterns and purchased books/patterns that people are done with. If you hask nicely they can shoce to help you or ignore you. When a pattern is out of print I don't think there is any huge ethical moral issue with asking someone to share it.