You guys wonder from where most of those weapons, ammunitions, rockets and explosives are flowing into Syria and the Middle East?
For example since the start of the Syrian conflict Bulgaria’s arms and ammunition factories work on a 100% capacity and even expanded their operations with doubling their exports and profits in a very short time. Bulgaria exported weapons worth a little over 1€ billion in 2016 alone with most of it going to customers in Saudi Arabia, Jordan, Iraq and the UAE... who only God knows what they use them for. The Arabs are a traditional weapon customers of Bulgaria since the times of the Cold War so the connections are there.
A similar thing happens in Serbia, Czechia, Romania and other such countries from the former Communist Block who produce cheap and effective Soviet style weapons and bombs. Cargo planes from Saudi Arabia and other Gulf countries have been spotted many times on airports around the Balkans.
In other countries with not much of an arms industry left but with huge stockpiles of old Soviet and Chinese weaponry and ammunition like Albania (and Bosnia as the member from there said) it’s the private contractors and weapon dealers from America who buy them and resell them to their clients in the Middle East or to the Pentagon. With some connections and a good bribe to the right people you can make a lot of money here on the Balkans.
Other source of weaponry is from the Black Market where you can again buy many interesting weapons even from Western countries as long as you have the money to pay and the right (mafia) connections. I have heard stories about the Civil War in Lebanon and how for example parties in the conflict managed to buy embargoed Beretta weapons with the help of Bulgarian commie officials who to this day controll all smuggling canals in the country and of course have good connections with colleagues from the Eastern Block, the Middle East. They brought the weapons and changed their serial numbers, then reexported them to Lebanon. It’s not that hard to do the same thing nowadays too.
If you can’t buy a thing with money, you will buy it with LOTS of money... and knowing the right people of course. The Pentagon and the CIA know that very well too. Not that I say they are the ones who coordinate this whole operation...