Sometimes I depend on the "nice but slow" people of the Borer Tribe down at the PH to drill out the middle of the chalk a little bit until it has a nice edge.
Sometimes desk people try to give me a nice new piece of chalk with the useless, flat top. I take a nicely broken in piece -- but not too deep -- from the box at the counter and say, "This one will be OK. No need to break out a new one." But mostly I carry my own chalk. If I start a new piece at home I use a dime, not a nickel, to start it.
I keep mentioning here about not drilling holes through the chalk and how no top player wears the chalk like that but the Borer Tribe has their Way and it is The Right Way.