If you're trying to find PC characters to buy regular ol' canon spice...you're doing it wrong.
Sorry to say but Spice is probably one of the most under utilized canon things in RP. Sure it's mentioned a lot, but off the top of my head I can really only think of two characters who I know use it 'regularly' and only one of those was actually RP'd as using it a ton. The fact is regular spice from canon just isn't that great, and lets be real most people don't really want to RP drug addicts.
Here's how you exceed at RP'ing a spice dealer as a character;
A. Sub a unique variant of spice that does other neat poodoo normal spice doesn't do. Several people have done this and said product was then used by several people, this is also way more effective because in theory your character could push this Variant of spice at all times.
B. Run your operation like a Cartel. You really don't need to actually 'sell' spice to any PC's, sure it would be neat, but it's not necessary. You can and 100% should expand your character's business through the selling of spice to NPC's, the funds from these sales should then be pushed towards other aspects. You can sub locations for labs, warehouses, ships to transport the spice, etc. Honestly RP'ing a Cartel is a ton of fun(I'm doing it right now), and it's really the most 'successful' way of being a spice dealer in RP.
These are pretty much the only viable options in my eyes, though there's always the third option of being the random spice dealer, and although that actually sounds fun to RP It's not really the way to create a spice 'business' since you'd essentially just sell small quantities that way anyway.
PS: Spice is actually huge in Star Wars. There is a massive galaxy wide market for dozens if not hundreds of different variants. Spice is literally Heroin, Cocaine, Acid, and even Pot rolled into one colloquial term. Spice was the lifeblood of several Hutt Empire's(You learn this in SWTOR and several comics). You absolutely can make a business out of it on SWRP you just have to do it right.