Well that is why they are so rare.
Chew on this:
Mod top cars are hot and super valuable, so they're in high demand, at least that's what I hear. There are plenty of mod tops with sixers and many have 318s so what gives? To find a 340 Formula S Mod Top is about impossible, Satellite Mod Tops are rare and so is anything else with a flowery covering.
I don't see why not the Charger be rare too, because if the Mod tops didn't have 'em they'd in the same boat you place the Charger sixer, right?
I don't think just ANY Mod top car is in high demand.
It goes like this regarding what people typically seek out for desirability/value for MY way of thinking and I believe this is what the majority of people in the hobby will agree. I am referring to the 68-71 year cars.
1. ENTER LEVEL DESIRED CARS: Muscle cars in general 340--426 powered cars
2. SAME AS ABOVE WITH PARTICULAR OPTIONS/COLORS
3. ODD COMBINATIONS OF OPTIONS
4. DOCUMENTED CARS
5. ODD COLOR COMBOS (INCLUDING INTERIORS, TWO TONES, MOD TOPS, ETC.)
An example would be the only KNOWN mod top A12 Super Bee. It has been know to have been totalled, sitting in a junkyard for years. Supposedly purchased recently and suspected that it is under restoration but is a well guarded secret. Someday it will surface all restored and people will make a big deal over it. However, the biggest part of the value/desirability will be because it is an A12 car WITH a mod top, not the fact that it is a mod top car.
Most people in this hobby are interested in muscle cars, not /6s, 318s, 4 doors etc. Now I am not dissing the owners of such cars, just pointing out what the bulk of the hobby is all about for the years above. Yes, there are other enthusiests for other reasons such as the C body crowd that typically buy their cars for different reasons such as trailer towing, room, comfort, etc.
My point here is that MOST people don't think /6 when they think Charger but rather R/T. This thought of /6 Chargers reminds me of the mid 70s after the performance era was dead due to insurance and fuel cost, when the factories tried to drag it out building 318 RRs with stripesand expected people to buy them based on a name and rememberences of days and cars gone by. The production numbers speak for themselves just as it does with the /6 Chargers. Not many wanted them then or now. I tell you that if I saw one at a car show I would be more likely to laugh rather than drool over it.