Landrace means a wild population that can sustain itself in a given environment without human intervention. All of the cultivars you mentioned are worked, human cultivated varieties, not landraces.
Most landraces are trash that you wouldn't want to smoke. The reason breeders look for landraces is that they have unique individual traits that might be useful when incorporated into modern lines.
Landraces are rare because of the drug war. Wild cannabis populations are regularly eradicated when they're spotted the whole world over.
Landrace is not a botanical name, it comes from livestock (swine in particular), it has been transformed into one by the cannabis community. Many of the "varieties" he mentioned are in fact regions . A strain that has conformed to a certain region and it becomes a landrace over a certain amount of time.
I have grown many landrace strains and I agree that many are not possessing great qualities. The only company I would trust with REAL landrace is the Real Seed Company. They visit certain areas and purchase seedstock from growers in that region.
they have seeds from the Kerala, Chitral, Mazar-i-Sharif, Thai, Malana, Moroccan....etc.
Much of the seedstock labeled and sold as landrace is hybrid. Even Durban is labeled as such and is nothing more than an early dutch hybrid. I do think there is a lot of African strains that are still explorable. I grew a nice plat from Seeds of Africa a few years ago from Reunion Island. Maybe worth giving a shot? Doubt you will find that strain still though.
One problem with South American strains as well as Jamaican (Caribbean) is the fact that Colombian genetics took over and polluted much of what once was.