It is possible to get 6 sockets in Path of Exile by using various methods. One way is to drop rare items, which can reward players with sockets and linked items. Other ways of obtaining sockets include using Harbinger to obtain fractured gear and by increasing the quality of an item to increase the chances of obtaining more links. Large-scale testing has shown that increasing the quality of an item significantly increases the average number of sockets obtained.

Using perfect fossils
Crafting with Hillock, or looking for divination cards are all ways to get higher quality on items in Path of Exile. Perfect Fossils can reroll the item and its quality between 0 and 30. Hillock can give armors higher quality up to 28 when he's level 3 and up to 30 when he's level 4. Divination cards can also be used to get higher-quality items, and some of the best cards are Chains that Bind, Celestial Justicar, and Dapper Prodigy.

Inspired Learning Card and Valid Side Areas
inspired learning card and that valid side areas are a great way to get six-linked items. suggest checking the Carrick vendor, Spider Lair, and Temple for divination cards. They note that opening a side area has been nerfed, but you still have a 10-40% chance of getting a crafted item from the end chest that is corrupted.

Conclusion
There are several ways to get unique items in Path of Exile, such as using a Vial of Hope to make them rare, using the Crafting Bench to re-roll corrupted items, farming Divination Cards, and running Incursions. All of these methods can help to increase your chances of getting unique items.