Perhaps easier than the mushrooms, various "chemical supply companies" will sell it to you for "research" and not ask many question. There's a list of such companies on the "RCSources" subreddit wiki.

It's definitely a good idea to get any chemicals tested before consuming them. I doubt they'd intentionally send you the wrong chemical, but I guess shipping mixups could happen. Energy control runs an excellent testing service https://energycontrol-international.org/drug-testing-service...

I'd try to Google a darknet Amazon.