The only seller I know of is GammaGoblin. I can't find any other vendors selling mescaline and was thinking of buying seeds and planting my own. Has anyone done this and what was the outcome? Is it hard? etc.
If anybody knows of a vendor with good mescaline (besides GG), I'd be surprised.
You could teach yourself organic chemistry, assemble all the necessary equipment, source all the precursors and synthesize it yourself in the time any cactus would take to grow from seed to flowering.