I know a few years ago I emailed them and asked if they would sell me a small label to fit a single motor case.
Their responce was they did not sell labels because people were putting them in cases and saying that the cases were original Purdey cases.
TEG London makes cases for Purdey and other London makers.
They can make you a case but not sure about a proper label.
What year was your Purdey made? And what is the barrel length.
Another option may be to contact Griffen and Howe as they are a U.S. agent for Purdey.