You're welcome, Lastest!
Efoj, it's hard to answer your question because I don't normally associate particular conductors or instrumentalists with psychedelics. That said, Stockhausen and his ensemble made a number of recordings in the late 60's and early 70's that might fit the bill -- Kurzwellen, Aus den sieben Tagen and some others. These pieces/recordings should be available via the Stockhausen Verlag (at a hefty price), but you can probably find excellent copies of the original Deutsche Grammophon issues in a good record store.
Speaking of Stockhausen, much of his compositional work from the mid-60's onward has an oddly psychedelic feel to it. Major pieces that immediately come to mind are Trans (a very weird piece indeed!), Inori (perhaps the most intensely meditative orchestral work of the 1970's) and Licht (particularly the earlier operas of the cycle; e.g. Donnerstag). I strongly suspect that Stockhausen tried psychedelics at least a few times in the 60's and 70's. On the other hand, maybe he didn't and the language of his later music really springs *only* from his highly personal brand of spirituality.
Anyway, some other composers and performers have definitely dabbled with psychedelics at some point, but I'd rather not give names... All I will say is that some are still with us, and some have moved on to meet the chef.
BTW, Celibidache was not one of them (he was a pretty strict Buddhist), but Gould was a notorious pill popper... but not into psychedelics, as far as I know. Cage was an avid mushroom collector but whether or not he consumed psilocybin mushrooms is unknown to me. I bet that he did from time to time though. One thing is certain: he enjoyed white wine.
