There are a lot of affiliate programs for shit like this, even growing mushrooms. I won't say how I know this but trust me when I say: stoners don't buy shit and they convert like shit. At least in my experience. I know it seems like a cool "niche" but it's not even worth the time IMO, I wouldn't recommend any of my friends to market it at least.
Nope, no money here. Stay out.
Like any niche you have to understand what makes it tick.
If you can buy bongs, blunt wraps, pipes, etc locally in cash, why would you buy it online and draw attention to yourself AND have to wait for shipping?
Price. This market is driven by price.
Find things that are vastly inferior in price online. This isn't too hard since many things stoner's buy locally have huge mark ups.