Ukraine has hundreds of 152 mm guns
But its shell factory could produce around 14-15K shells / year (that's it, during peace time)
Let's say (very very conservative number) around 500 tubes
You end up with 30 shells by tube produced / year
30 shells for high intensity warfare is very low
The neighbor provided all what they had in152mm but they don't have anymore themselves
While there is plenty of 155 mm stockpile and prod capabilities are bigger (it is a NATO standard afterall, could be produced anywhere from USA to Israel to France, UK, Germany and whatnot)