Production of munitions is constant, and is happening in several countries. This is a dynamic situation, not static.
The production rate is still lower than what Ukraine wants to use.
What’s getting shipped now are 155mm DPICM shells (look it up). These could be good substitutes for 155mm HE for a lot of uses, especially counterbattery and shooting at tanks, as they are armor piercing bomblets. Not so good against bunkers or buildings. The US has to dispose of them anyway.
What could also get shipped are the M26 cluster munition (look it up) for the MLRS/HIMARS system. Those things are devastating. At one time these were the principal ammo for US rocket artillery. I understand the US has vast numbers in stock.
Granted, Ukraine has few HIMARs or MLRS launchers, as they were supplied to shoot precision GMLRS GPS ammo, not as general purpose artillery. But originally the MLRS was actually the US answer to the Russian rocket artillery as an area effect weapon - the Grad, Uragan, etc. That’s why the US has about 1000 redundant MLRS systems it could ship. Every US Division had at least a battalion of MLRS.
The DOD is saving those for use against American citizens.