Any garden store should stock gypsum as a powder.
Cal-mag for human consumption is the carbonates, aka dolomite lime. That's again available in bulk ... at garden stores, but as an insoluble mineral it is again only good for soil.
If you cannot get cal-mag, what nutrients are you using?? cn
im using a locally made organic one with micro nutes
but i wanna have calmag for future use if needed specifically
i havent seen gypsum in every garden store ive been even in True Value even dolomite lime if they had they sell in bulk like 50kg-1ton minimum[ive tried to buy some retail but they wont sell damnit]
btw im an asian in a 3rd world country. farmers here use crap chemical ferts thats waaay off charts to use for mj, crap everything, organic sources here are hard to find even if our main source of income is agriculture. if there are its too damn expensive like the pre made additives ive found and they sell it for like $15/2kg well, except for uncomposted chicken/farm shit, bat guano[that isnt real bat guano], worm castings[im working on it, pre made ones they add chemical additives], charcoal, burnt rice hulls. literally all stuff here they sell/know about are in "general" like if its "fertilizer" its good for all plants lol
i envy you guys!