You can buy the precursor, niacinamide riboside, from at least a dozen outfits. They all buy from a single supplier. Cost: $40/month.
Or buy niacinamide, which has hundreds of suppliers, at one tenth the cost. But it may take ten (or more) times as much to have the same positive effects.
I’ve come to believe that marketed derivatives of niacin, or variations of vitamin B3, are more of a scam the greater number of steps they diverge from niacin. But at least they aren’t so likely to cause diabetes, etc.