We cannot endorse or list sources publicly as per site rules. While some DM for sources, it's unclear if the rule applies to private messages as well. I see a lot of brazen "Hey, could you DM me for some sources?" but those don't get banned, so do what you will with that.
I know precusors and chemical alternatives to SN, but I can't say since it's uncharted territory and quite frankely, I think we should milk SN as much before it gets restricted before moving on to alternatives.