If you must use an all electronic version you could use a power PNP to light the LEDs:
I did not test this, but I don't think there are any reasons why it wouldn't work... It also is an example of a circuit that I don't really like but it's quick and dirty.
R1=1.5K ohm, 1/4 watt
Q1=any high current low voltage PNP-Darlington like TIP125. You may be able to get away with a non-darlington with 560 ohm, 1/2W resistor and a crappy transistor like a TIP42.
all other components are as you need. May have to tweak some of the values/transistors depending on your load.
I did not draw in the rest of the 555 circuit.
P.S. : Having blue lights on your car can get you ticketed. If you get a ticket for impersonating a cop, don't say I didn't warn you...