Hill Street Blues

There are diecast 1974 Monacos you could use if there are no other options.

Not a lot of police car kits available for the late 70's through mid 80's. I don't remember if the cars changed over the years of the series, but I know there is no 1977 Dodge Monaco Royal kit.

 

There is a 1978 Dodge Monaco police car kit (TJ Hooker, Dukes of Hazard, Joker Goon Car / Gotham PD) it is a smaller car, but is similar in appearance so could work if you are not super fussy about being completely accurate. There is a 1/18 Diecast "Blues Brothers" 1974 Dodge Monaco which might be closer since it is the larger body style.

 

Not really a lot of other options, there only a handful of police car kits from roughly that period out there. A 1970 Ford LTD (AMT / Ertl), a 1980's Chevrolet Caprice (resin from Modelhaus), a 1989 Ford Taurus (AMT/ Ertl), a 90's Chevrolet Caprice (Revell?) and a late 90's Ford Crown Vic (Lindberg). Diecast provides a little bit more but not much.

Unless the later seasons used a Chevy Caprice, I'd say the 1978 Monaco is the best option.

I did a little research for you after ajlafleche's posts, and found out that the car in question is a 1977 Dodge Royal Monaco, at least according to several different sites.  I can't find where a model kit of that was made though.

I don't remember ever seeing a tie in model for that show. Best thing to do would be to watch an episode, determine what car it was and see if there's a kit of the basic car. Then, shop Chimneyville Hobbies and see if they have similar light bars and markings.