I just finished Dawnguard but now I need a constant supply of Elven Arrows to use for Auriel Bow. Is there any way to craft them or is there a place where they constantly spawn? Any help would be appreciated.

You can craft any arrow at any forge with a bit of firewood and refined moonstone. It comes it packs of 24.

You can craft them with moonstone and firewood with the elven smithing perk, or you could use the guard in solitude. If you don't know how to do that, just look up "Arrow dupe solitude guard" on youtube

The blacksmith at the Vamp Castle and Sourine Jurard sell 200 Elven arrows at all times after you finish the QL