I don't have a direct source I am afraid, but have been researching building a light recently and have come across a couple of resources that may be useful if you don't already know them:
a member of this forum Max Mekker has a
website which he details a 35w HID he built, the only catch being it is in norwegian.
otherwise you could follow the links or ask questions at
msn groups
the other resource is
airspeed press who publish a book on building dive lights and have an extensive list of component sources
Best of luck, Ben.