We don't have synonyms for russias yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are russia, Russian and russians.
(n) :
(chiefly historical) The East Slavic states descended from the Rus collectively, typically including Russia (Great Russia), Belarus (White Russia) and Ukraine (Little Russia or Kievan Russia); the Russian Empire. Especially in the title "Emperor (or Tsar or Czar) of All the Russias."
(n) :
(chiefly historical) The East Slavic states descended from the Rus collectively, typically including Russia (Great Russia), Belarus (White Russia) and Ukraine (Little Russia or Kievan Russia); the Russian Empire. Especially in the title "Emperor (or Tsar or Czar) of All the Russias."