North
In healthy discussion about all opinions about this subject, here's another opinion: naturally present probiotics in food have apparently not been enough for me and others, and for those people, seeking capsules or other supplemental probiotics may be a wise move.
There, now as to your specific question: There is a company in South Carolina called cocoon nutrition. So far they've been the only source in the US I have found. But you have to call them on the phone to see about getting the Mutaflor, as they do not advertise it on their own website, for some reason.
I HOPE OTHER COMPANIES CARRY IT SOON -- we really need more sources for this stuff, or for other makers to start making it so people can try it...it may not work for everyone, but at this point hardly anyone can even try it with it being so hard to find.
I ordered it by phone, and now own it. Have only taken it once so far, and then had to travel and didn't take it with me on my trip, so could not do a continuous experiment yet, but am about to try it again.