Well LED's will be out of the picture as your car will display a bulb out WARNING sign that will not go away untill you replace tem with normal filament bulbs. You can buy RESISTOR kits to make them work but they don't normally work or don't work for long as either the ECU "freaks out" and makes them stay on when the car and lights are completely switched off or the resistor overloads and the warning comes back.
The only ones i can suggest that a good enough to match Xenons are from AUTOBULBS DIRECT
SUBARU IMPREZA 501 W5W CAR SIDELIGHT XENON BULBS on eBay, also Bulbs Lenses, Lights Lighting Accessories, Car Tuning Styling, Cars, Parts Vehicles (end time 03-May-08 19:40:56 BST)
I have these in my car and they more or less match my 5000K headlights which are more blue/white than your factory fit lights. I have tested many side light/headlight bulbs and these are the only ones that aren't yellow and that included phillips bluevision/silvervision etc.
Hope this helps. Joe