Agree with cxdom in that they are probably the oldest and largest producers of eliquid in the world.
I vape a couple of Hangsen tobacco flavors, mostly DIY but some pre-made.
For small quantities you can try Fasttech, $9 and change for 100ml bottles. The flavor might vary from order to order because sometimes they send you a batch made in Europe and sometimes they send you a batch made in China (Hangsen has two factories).
For really large orders, try Zainy. They ship it straight from the Hangsen factory in China (I like the flavors from the China factory best). Shipping is expensive though for small orders.
I'm not a fan of the Dekang tobacco flavors I've tried, though I'd like to try their RY4.