Hi GN
Normally bought in, in my experience.
Some of my locals use 30/40 kilo drums of KTC or Balah brands, depending on their business.

Commonly Pataks 2.2L catering size are used.

Food colouring is used to change its look in some places.
I'm into Geetas Premium at the moment, good blend and full of Kalonji seeds.
Hope this helps
cheers Chewy