In this regard, where do I get the artifact weapon for druid?
You can get your first Artifact Weapon quest in Dalaran after you complete the Legion introductory quest chain. A member of your order will approach you and offer a quest to get your first Artifact Weapon.
Furthermore, can you Transmog weapons to look like artifacts? Artifact Transmog in Shadowlands - New Creative Weapon Combinations. With these new rules, you are able to transmog any artifact appearance from your class, as long as it follows normal weapon transmog rules (i.e. 1-hand to 1-hand, 2-hand to 2-hand, etc).
Also, can you still unlock Legion artifact appearances?
Challenge Appearance
The other tints can still be unlocked if you finished the Mage Tower Artifact Challenge during Legion.
Can you still get artifact appearances?
When patch 8.0 went live, the Mage Tower Challenges on the Broken Shore were removed from the game. With the exception of the appearances and tints associated with that challenge, all other appearances are still available to earn.