producing kefir grains from commercial kefir?
The dynamics of the Grain growth are not currently well understood, much less its formation. Some researchers attempted to create grains in laboratory, but failed.

There are over thirty or fourty strains of microbes in the kefir, and their ecological relationships are very complex. One could call the whole kefir culture an ecosystem of its own.

The grains grow either because the matrixes of existing grains entice the microbes to create more grain matrix, or because there are specialized microorganisms inside the grain that are responsible for creating more grain.

What is known is that the grains need Kefiran to grow, and Kefiran needs Alcohol in its synthesis. Commercial cultures of kefir often omit the alcohol-creating yeast for obvious reasons, so it too adds to the impossibility of getting Kefir grains from commercial kefir.

Either way, the fact is there grains do not come into being on their own. New grains are split from existing grains.

There is a small possibility that a kefir culture from grains that was strained could form new grains, but its not confirmed.

The commercial cultures are sold with around five to ten strains, much less than full blown kefir grains. They won't form grains, since the strains were hand-picked in lab by their function, and probably the grain-forming ones were left out.