Vendor talk is not allowed. LSD is rather illegal in the US. I'm sure there are people buying and selling it over the mail, but you're not gonna find illegal drug hookups on BL. If anyone here knows of an LSD by mail hookup, I doubt they'd want to share any information about it on a public forum.
Personally, I would be extremely skeptical of anyone claiming to sell LSD by mail. At least with RCs they are technically legal businesses and you can check into their reputations. If you know the connect well, best of luck, but I would never send money to someone I didn't know well personally for acid by mail. Plus, wouldn't it degrade in the mail?
Also, the SWIM talk provides absolutely zero legal protection and just makes you sound silly. Anything you wouldn't admit to doing yourself, don't post about your friend or SWIM or whoever who did it. No jury on the planet will buy it isn't about you if you say something truly incriminating. Discussing things in hypothetical terms is usually safest. There's no need to mention what illegal substances you have or have access to in order to ask whatever questions you have. Little slips are no big deal, it's not like the DEA will hunt you down because you mentioned you have one hit of acid in your drawer or something, but discussing things like bulk supplies of acid is probably not smart.