A couple suggestions:

http://phish.com/tours/

http://www.widespreadpanic.com/tour

Also, pretty much any large multi-day music festival with a campground, especially reggae. Suppliers are way less discreet at these kind of venues. You'd typically either get lucky and get whatever they say it is, or not and get something that has no effect; chances of something dangerous are low.

A few shady chemicals (NBOMes) have been circulating as LSD and they are dangerous[2], especially when you're expecting LSD but there is a way to be more sure of what you're taking[1]. 1: https://www.erowid.org/chemicals/lsd/lsd_testing3.shtml 2: https://erowid.org/chemicals/2ci_nbome/2ci_nbome_death.shtml

Only one person on this comment page to mention the biggest problem LSD faces today. NBOMes.

Discovered only a few years ago, it's way too new and untested. The effects are not the same as LSD, and reports of negative side effects are common.

Unfortunately they are commonly sold as LSD. Very sad and worrying.

If you're in the Bay Area and ever want to attend a Phish show (or other good jam band), I'd be happy to introduce you to the scene. It's been a life changing experience for me and an integral part of my life for the last 15 years and am always happy to show people around.

Trance party. Psytrance, not Armin van Buuren trance. :)

You can, but you'll have no idea what you're actually getting. It may or may not be LSD, and it may or may not be mixed with something else.

You ideally want to develop a trusted source, probably through someone you know

And yet that's exactly what people do allegedly. Well, it helps to not ask openly around until you trust the other person somewhat (which even means getting to know them for a while).