$6 billion is nothing to the Russian economy. Russia spends far more in helping foreign states to be in their political sphere. As I stated 80% of Russian export is made of oil, gas and metals. The entire world purchases Russian weapons. These are Afghanistan, Syria, India,China, South America, Egypt are equipped with Russian weapons or copies of Russians weapons.
Croatia is a NATO member just like Poland or Slovakia. But don’t be fooled that USA or UK will sell Croatia weapons or Croatia will be able to afford American planes. At best USA will offer a military base in the Balkans.
All powerful countries of the world produce their own weapons – Italy, France, UK, Israel, Russia, USA. The rest are purchasing weapons from few countries.