FYI, i have put kefir grains in the fridge for almost a year, and rejuvenated it.
I really dont think it matters from what source you purchase, kefir is very tough in that they have done experiments to try to put alien bacteria and yeast in the grains and the grains will go back to its original flora and kick out the invading flora, so by knowing this it will bring comfort to know that it doesnt really matter whom you purchase from just as long as its alive.