XKs Unlimited is a really nice shop in California. They are also a Shelby continuation dealer and as such the parts guy out there is quite familiar with the Cobra. I got some SW gauges from them in the past.
you can find them on the web at
www.xksunlimited.com
I would perhaps do this transaction on the phone and talk to the parts counter guy and insure that they are in stock. They advertise the PL headlamps all the time in CLASSIC MOTORSPORTS magazine (formerly BRITISH CAR).
XKs has a wonderful catalog for Jaguar parts.
Hope this helps you out.