I have seen people use these arrows on youtube but where can you get them from?
As per the The Elder Scrolls Wiki
- Enemies that wield bows, such as guards and bandits, drop arrows
- Arrows can be purchased from Blacksmiths in limited quantities. Arrow strength is contingent upon Character Level. Arrows in larger quantities can be purchased from Fletcher in Solitude or The Drunken Huntsmen in Whiterun.
- With the implementation of the Dawnguard add-on, arrows can now be crafted at a blacksmith's forge.
- Arrows are notably farmed from guards doing target practice (though they only use steel arrows)
Also: Ebony Arrows
- Starting around level 40 ebony arrows (along with all other ebony goods) become available in good quantity from blacksmith merchants such as Eorlund Gray-Mane or at Warmaiden's.
- Enter the Labyrinthian and clear out Lost Valkygg. The Draugr Lord at the end next to the exit always carries an Ebony bow and a large quantity of arrows, regardless of level.
To add to the current answer:
- Ebony Weapons appear in leveled lists (as loot or enemy item drop) starting at level 36 (enchanted varieties at level 37).
- Arrows can only be smithed if the Dawnguard plug-in has been installed.
- With Dawnguard, it becomes possible to craft standard arrows using 1 piece of firewood plus an appropriate metal ingot.
- Ebony Arrows can be forged using the Ebony Smithing perk.
- Ebony Smithing requires 80 Smithing skill.
- 3 Ebony Ores are obtained by mining Ebony Ore Veins. Cannot be purchased.
- 1 Ebony Ingot is obtained by smelting 2 Ebony Ores. Can be purchased at level >= 27.
- Ebony Ingots may be sold by blacksmiths and general goods merchants starting at level 27.
- Ebony Ore may be randomly found in Falmer loot starting at level 13.
If you character has reached a sufficiently high level, Nordic Ruins become the best place to collect ebony arrows. If you are leveled high enough, most of the enemies in Nordic ruins will be Draugr Deathlords. These enemies use ebony weapons almost exclusively. Roughly 1/3 will be one handers with a sword or war axe and an ebony shield, roughly 1/3 will be two handers with any one of the two handed ebony weapons and roughly 1/3 will be archers with ebony bows(and corresponding arrows).