You can buy a used set of OEM HID Projector - version 04-09 Rx330/350/400h headlights and do the conversion. The bolt patterns are the same.
You will need to do some hardcore wiring though, as the plugs will be very different. You'd need to splice the wires going to your present halogen low beam bulb, and wire them to the HID headlight ballast. The 12V will activate the ballast which will illuminate the HID bulb. No extra harness required, as there's enough current there. Then splice your present high beam bulb to the HID headlight's high beam bulb, which is the same.
You will also lose the