As I am no authority at all on Chronomatics and I have none, I'll leave to much better suited people like our host Jeff to answers your questions thoroughly.
However a few hints that I've gathered from Arno Haslinger's book on Heuer chronos and Jeff's own article on the topic, while we all eagerly await for Jeff's knowledge:

- the name was used for a very short period, just months. Afterwards Mr. Jack Heuer very graciously agreed to a request of his friend Willy Breitling's to leave the name to Breitling (Chronomatic must have sounded a very nice evolution of Chronomat!), so Heuer switched to "Automatic Chronograph".
- the number consequently is very low, probably in the hundreds at the highest: Jeff, what do you know about it?
- where are they? I surely don't own any, I have seen a couple 'live' but I'd expect the bulk to be in the safe custody of OtD members ;-)

Cheers

Fabrizio