Where can I buy this yogurt?!

Most yogurts sold at stores still do "contain live cultures" in them (look for those exact words on the label, not the words "made with" live cultures, and/or look for the "seal" from the American Yogurt Association or something like that).
Some "yogurts" however started out with live cultures but the manufacturers killed them from using too-high heat while processing, etc...those "yogurts" are basically then just pudding.

The benefit of eating yogurt IS the live cultures, so you do want to be sure you buy yogurts with the cultures still alive if you want to get your money's worth (and your health's worth too).

The beneficial bacteria (cultures) in yogurt and in similar fermented milk products are very good for the (whole) gut, and can help with all kinds of gut problems from stomach to intestines (including regularity, helping with various bowel diseases and difficulties, etc) as well helping the immune system in general.
Yogurt is usually fine for those with lactose intolerance too (because the cultures have eaten up a lot of the lactose and turned it into lactic acid).

If you want to read a bunch more about yogurt, why it's healthy to consume, ways to flavor it and even make your own, and more, check out parts of my replies answers in these previous questions:

flavorings & making your own:

and maybe some of the stuff here too:

here in uk they sell it in supermarkets along with other yogurts