Yohei, you had a great idea here. Thanks. I picked up my parking lamp leds from
superbrightleds.com The type 168 (replacement for W5W), 2nd from the bottom, worked perfectly for only $2.99ea. They add a whole new look, especially used in conjunction with the HIDs.
While I was at it, I ordered an extra and replaced the dome lamp, which also uses the same bulb. It adds a nice, soft touch to the interior. Note, you need to remove the entire dome light housing; the black frame shown below, and not just the bezel (you'll wish you hadn't). Use a thin screwdriver to pry the right side of the housing and release the clip. It's a pain in the arse, but I figure I'll be long gone before that LED burns out.
Super Bright LEDs has boatloads of other automotive LEDs, including LED flasher relays for only $13. You can probably upgrade your rear panel stop/park lamps for less than $40 bucks. I ordered in the morning and they shipped same day.