Visibiome has OTC and rx-only probiotics products, the latter of which is used to treat severe IBS and ulcerative colitis. Their OTC products are also very high potency and regularly recommended by doctors as well.

Also, nicer grocery stores typically have a refrigerated probiotics section, and those are typically good brands as well (Garden of Life is one). Generally, shelf stable probiotics are less potent and varied in cultures than ones requiring refrigeration.