Years ago there was a person at the DuPage show that offered rechroming services. He had a rechromed 356 Silver Bullet as a display piece. I think he was actually having vacuum metalizing done rather than rechroming on the plastic shell. The engine looked far better than anything that ever came out of the Gilbert factory. The cost was a major barrier.
There are firms that will do rechroming of plastic toys but from the costs I have seen it would be cheaper to buy like new originals of these cars.