Sorry, I don't know where these artists get ground chalk.  I have never used it before.  But chalk is basically calcium carbonate.  So one option may be to purchase calcium carbonate from a chemical distributor such as VWR or Fisher Scientific.  Pure chemicals, in small quantities, are not particularly inexpensive.  So the larger the bottle or drum that you buy the cheaper it will be per pound.  Now, I have never used pure calcium carbonate in place of "ground chalk."  Heck, I have never even used ground chalk before.  So I don't know if this would work.  Chalk may have some other mineral impurities in it whereas calcium carbonate reagent is essentially pure calcium carbonate without these impurities.   Anyway, this is my perspective, as someone with a chemical background since it appears as though you have been having trouble finding an answer to your question.  Here is a link to VWR's website for calcium carbonate.  If you decide to go this route I would suggest simply using the least expensive product you can find:
http://www.vwrsp.com/psearch/Controller … rtgrp=null

Whiting = Ground chalk = Calcium Carbonate.

I just spoke to a local supply of fine art and pottery supplies.  They said they can order it for me in one-pound, five-pound and larger amounts & it is very cheap.  (Ahem!  "Inexpensive")

They said they get it from a place in Tacoma, WA, called the Clay Art Center, but they are sure there must be other suppliers around the country.  And England.

It is apparently used for painting and for pottery, so you might try checking local sources for fine arts materials.  I doubt that Michael's & others like it would have it, and if they did, they probably wouldn't know it.  (Did I hear a sneer just now?  I'm not sure...)   :shock:

Sue

I have wondered if Kilz primer could replace gesso for surface smoothing effects?

Sue

Sebrink, the expensive version is a pigment for paint.  You don't need that. 

Here are some of the things it's used for, maybe it will help:   Plastics, rubber, coatings, inks, adhesives, and soil conditioner, building products, plastic filler, ceramic flux, asphalt filler, chemical processing, glass ingredient, water treatment, pesticide granules, dusting agent, welding rods coating, thermosets, thermoplastics, paints, coatings, adhesives, sealants, rubber, pharmaceutical, toothpaste, and food additives.


Sue