External funding is unimportant if you have control over a closed economy with no goods imports. In that case money import is really just paper import.

India helped Sri Lanka to embargo LTTE and the LTTE blockade runners were defeated by a Sri Lankan small fast boat armada (built in the country iirc).
They had sunk the last LTTE weapons & ammunition smuggling ships just months before the final battles.

That didn't mean much more than a weaker conventional posture of LTTE, though. Sri Lanka could as well have won (with more bloodshed) by focusing its resources on the army.