According to some comments in the DC Forum, and confirmed by poking through hatcheries, it looks like at least four breeds can produce the "shiny" Copper alt: Astrapi, Bolt, Electric, and Thunder. There may be others!
To get the 'shadow' of the new Cantor alts to appear on your Encyclopedia page, use Ward and Earthquake on a Cantor egg. I think it works even if Earthquake kills the egg, and presumably works even if you go on to incubate/otherwise change the outcome of the Cantor egg you Warded. I bred a random Cantor to test it, and the shadow appeared as soon as I Warded the egg, and didn't disappear after I abandoned the egg.
Additional info: New Copper alt, new Cantor alts
To get the 'shadow' of the new Cantor alts to appear on your Encyclopedia page, use Ward and Earthquake on a Cantor egg. I think it works even if Earthquake kills the egg, and presumably works even if you go on to incubate/otherwise change the outcome of the Cantor egg you Warded. I bred a random Cantor to test it, and the shadow appeared as soon as I Warded the egg, and didn't disappear after I abandoned the egg.