Seems that it has become fashionable in the expat community, and the question of where to find made it to the list of “top 5000”.
It pops up all over the place in an unpredictable manner but you will **always** find it in the Old Believers shop at Rogozhsky Poselok 35(?).
It is next door to the Old Believers cafe which is open to the public regardless of faith and is highly recommended (a) for Russian food properly understood and (b)as a place that turns near-totally vegan Wednesdays, Fridays, and during other periods, usually preceding celebrations.
Recommended for fresh vegetables or soup of light/yellowish colour **after** it’s been poured into plates both as seasoning and decoration. Milder than regular salt.