Try HiDplanet : The Official Automotive Lighting Forum
Honestly you are probably going to have to be on the lookout for a wreck and get them from there or pay a ridiculous amount for a new OEM replacement.
Or you can try a set of Philips Xtreme bulbs or OSRAM
(not Sylvania) Silverstars.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.