Making your own ballast has the same satisfaction that a gardener gains from making their own compost!
You may not be able to use my technique as most of the material was given to me so, I do not know of a commercial source.
I started off many years ago using grey (or pink?) cat litter, ground down or sieved to a fine grade. I would not recommend cat litter now because the granules tend to fall apart when wet. But, remnants still show up in my ballast because my mix is reusable from layout to layout. (Read on and you'll find the special glue that holds the ballast stable yet allows it to be lifted and re-used). Subsequently I was given a bag of decorative grey (granite?) chips use by the building trade. The granules are a few millimetres across. These were crushed in an old coffee grinder and sieved with a fine mesh tea strainer to remove the dust (which is used for tarmac road surfaces) and then sieved with a 1 millimetre mesh used for car body repairs to create scale 3" ballast rocks.
Cork granules were sieved and added to the mix in small quantities. The grey chips predominate and the cork adds a little colour variation.
The magic glue is wallpaper paste flakes that are crushed and sieved with a tea strainer with the resulting 'dust' added to the mix. Can't really say what proportions are used - it's all guess work.
Some prototype track work has dark ballast between the sleepers where trains have deposited oil and muck so, a second mix is made up comprising the granite chips, black carbon granules from a face mask filter and dark brown dyed sawdust (Peco scatter material). The photo above shows this variation.
The ballast is then laid and water mixed with a little washing up liquid (to reduce surface tension) is sprayed to thoroughly soak the material. It takes a couple of days to dry by natural evaporation and leaves a stable surface that will withstand light vacuuming but will crumble to pieces if scrapped with a screwdriver. Hence it can be broken up for reuse.
To Part 7