Hello DIYers

I'm building a flood and drain system and have settled on granite as my media of choice. The river rock in my area was my first choice but it bubbled in vinegar. My problem with the granite is the availability of suitable sizes. I'm looking for 3/4 inch rock. The granite labled 1/2 inch contains many smaller pieces, and the granite labeled 3/4 inch contains many pieces that are 1 inch or even 2 inches.
Any ideas or suggesdtions?