We don't have synonyms for calibres yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are caliber, calibre and Calidris.
(n) :
(UK, Ireland, Canada, Australia, New Zealand, etc.) Alternative form of caliber. [Diameter of the bore of a firearm, typically measured between opposite lands.]
(n) :
(UK, Ireland, Canada, Australia, New Zealand, etc.) Alternative form of caliber. [Diameter of the bore of a firearm, typically measured between opposite lands.]