During the Wano arc we discovered that the CP0 bought weapons from Orochi and Kaido. Previously the CP0 passed through Doflamingo but found itself forced to deal directly with Wano’s Shogun after the fall of the Shichibukai.
But why does CP0 need to buy weapons from a pirate? After all, the World Government surely has its own arsenals, and the weapons used by the marines certainly do not come from Kaido.
In reality, the weapons that the CP0 purchases from Wano are not intended for Marines or agents of the World Government, but for factions secretly supported by the World Government.
The World Government and the Revolutionary Army are waging an indirect war, a so-called “proxy war”. Instead of directly confronting each other, each of the two parties defend the governments which support it and seek to overthrow the governments which are unfavorable to it, provoking coups d’etat and revolutions. And each of the two parties sends weapons and sometimes fighters to their allies. This is the reason why the Revolutionaries store a large quantity of weapons in their base.
This is the reason why the World Government buys weapons from Doflamingo: the World Government is not supposed to intervene in the policy of the member countries, so if it sent in these countries weapons made for the Marines, the countries concerned would quickly understand that the government is intervening in their affairs. That’s why the CP0 needs Kaido’s weapons, the origin of which is untraceable.
This is also the reason why the Revolutionaries wanted to discover the origin of the weapons sold by Doflamingo: they realized that a large number of these weapons were used to arm their adversaries. If they can destroy the source of these weapons they will take a considerable advantage in their war against the World Government.
This is what happened after the fall of Doflamingo: many factions were forced to lay down their arms, causing the end of many wars around the world…
…and the victory of the Revolutionaries.
And CP0 is now trying to recover lost ground by purchasing a large quantity of weapons from the Shogun.
*Theory by Albrede