Dear Johannes,
They have a large collection of these orchids at the RHS garden at Wisley.
So it might be worth contacting them.
A forum member, Paul, who writes the Wisley log, (under the name of 'Wisley') would probably be able to help you.
Try emailing him.
He did a special diary entry on these orchids last year: go to the main SRGC website, and look at the Wisley Log Archive : Log 16, 31st July 2008.
