Yes, I myself know only one such disk – from burial-place of Celtic war chief, MLT, circa early III Cent. BC, near Chiumeshti, Romania. The time of the rich in armour burial is exactly correspond to the great Celtic invasion to the Balkans, and some Ukrainian archaeologists ( Voznyak, for example) are thinking that war chief from Chiumeshti burial might be famous Celtic chieftain Cambavlos himself (!!!), which has been mentioned by Pausanius, X, 19. But this idea, undoubtedly, is conjectural and extremely disputable. And this disk quite might be as some horse harness part too:
However, as I think, such cardiophilaxes are might be in Celts` hands, even if theoretically.
The matter with cardiophilax for my Celt figure is that: I don’t like to make him with chain mail, but without any armour the miniature will be looked very simply and uninterestingly, to my mind.
Maybe my Celt with cardiophilax on his breast is will not be a terrible historical error?
Many thanks for your nice Hallstatt Celt reconstruction.
Best wishes.