Life Extension dot com is and has been the cutting edge source for nutraceuticals. Great company, but expensive for everyday stuff....
I do use their 5-LOX Ashwaganda product for my RA, which I suspect, like NAC, would help Long Haul Covid19 cases...for the same reasons. I take about 6 of their specialty cutting edge, best of the best products...
They even have one that is a Cytokine Suppress product, with a Chinese Bean and Green tea EGCG extract (EGCG is good the brain)..