Alice,
I suspect you won't be able to source this part - I looked at the manufacturer's web site and my guess is that if you're ready to place an order for 5000 of them they will reply to your mail.
Taking the specifications they give with an input of 230V (1.7A) and a variable output of 230V - 11.4V I searched around for an alternative. Thousands of 230V in to 12V out dimmable transformers but not a sign of anything like the one you need.
I think you're out of luck unless you want to re-engineer your lamp for low voltage bulbs.
Sorry...
Peccavi, February 2009