"New supply has decreased paucity"
is awkward, and potentially unclear, and at least arguably incorrect.
One could write
The new supply has decreased the paucity of food.
However, that is a somewhat stilted expression. Better would be
The new supply has decreased the shortage of food.
The food is no longer in as short a supply, with the new arrival.
The food is now more plentiful than it was.
I would not use paucity when describing a change in the level, but only to describe a static condition of shortage.
One might say
There has been a paucity of food since the drought.
There is a paucity of registered socialists in the US Congress.