S. Boulardii is "Florastor". I ordered mine from drugstore.com on Amazon because it was cheapest there. You can buy it on the shelf in your pharmacy/chemists. It doesn't require refrigeration.
It has an interesting history.
from this website
florastor.ca/florastor-information/what-is-florastor/Origins of Florastor:
Florastor (Saccharomyces boulardii lyo) was discovered in South East Asia in 1923 by a French scientist named Henry Boulard. He worked to isolate the yeast from the skins of various tropical fruits (lychee and mangosteens) after having observed that the indigenous peoples used the skins of these fruits as an antidiarrheal medication. Since the discovery of Florastor, over 80 clinical and pharmacological trails have been published proving the many benefits of Florastor. Today, Florastor is sold in over 90 countries worldwide. Medical Futures Inc. is proud be the company offering Florastor in Canada.