It's always 'ringer', Vil.
I found this for you:
A dead ringer
Student or Learner
Would you be kind enough to tell me the etymology of the phrase “dead ring of somebody”?
She was dead ring of me.
Billy the Kid and his dead-ringer look alike who shows up after the Kid has ...
dead ring of somebody = the dead spit and image of somebody
Thanks for your efforts.
I can't say that I have come across 'dead ring' either.