We've had scrap metal full size Aliens and Predators, a full size X-Wing, but none of these have been working. This replica does. Through Boing Boing on Ebay:

"MAD MAX INTERCEPTOR"
FORD FALCON 500 XB 1976,"EX VICTORIA POLICE INTERCEPTOR"
351 2V 600 HOLLEY,FMX AUTO,9 INCH DIFF 2.75 GEARS,GT SUSPENSION
SENT TO SPECIAL VECHICLES OPERATIONS,S.V.O FOR PERFORMANCE MODS FOR VICTORIA POLICE DEPARTMENT
YELLOW RED & BLUE FRONT SPOILER,ROOF SPOILER,FLARES,LIGHTS AND SIREN
GOOD CONDION ,VERIFICATION LETTERS,MFP NO. PLATES

Unfortunately the sale has ended...but the good news is that the reserve of $20,000 (Australian) has not been met, that means you're still in with a chance! Might not be that real though...check out the Q&A; from the seller:

Q: was this the car in the movie? If not, How close to the original movie car is it? By the way I know where there is an original front end to suit the black interceptor if youre interested (better than the copies made these days). Its on a restorable xb coupe. The guy also has the correct roof and boot spoilers and a fake blower set up. I didnt ask if it was for sale but I reckon it would be at the right price.

A: has verification paperwork from ray beckerly/the vechicle designer on the movie and from steve millchamp how played "roop"the previous owner sold all the other stuff off .he had the blower ,mask with pop out eyes,jacket,battens and gooses helmet

Oh yes! Get me some of that 5.8 litre!