You could try brightheadlights.com. They sell HID conversion kits. You will have to add new ballasts and ignitors. I am not sure that HID fogs would not defeat the purpose of the fogs. Yellow cast works better for visibility in fog, but if its asthetics your concerned about I am sure it can be done with the proper setup. Voltage is usually different for fogs so make sure that you get the right kit and I would also make sure that the lense cover can withstand the heat and not melt. You will also need to know what kelvin temp you want. CATZ is a good brand I have them in my Denali.

Let us know if you find anything else.