Make your own! All 4 of those foods are surprisingly easy and cheap to ferment yourself. The best books on the subject are by Sandor Katz. There is lots of information online as well.
I drink homemade Kefir (with a bit of honey) every morning. Whether the effect is real or not, I feel better on the days I have it than the days I don't.
I chose Alex Lewin instead of Sandor Katz. Now I have this sauerkraut that smells pretty good, but I don't have the courage to eat it or the confidence that it isn't moldy. If I had chosen Katz would things be different?
I drink homemade Kefir (with a bit of honey) every morning. Whether the effect is real or not, I feel better on the days I have it than the days I don't.