One of my 5e characters is a Longbow based archer (Wood Elf Rogue 2/Fighter X with the Sharpshooter Feat), with her weapon of choice selected primarily for flavor reasons. It's a little annoying that in most adventures (i.e. where the Longbow's additional range doesn't matter much) she is sub-optimal with regards to DPR when compared to a Hand Crossbow based build with Crossbow Expert and Sharpshooter.
Is there anything in the game (either character options or magic items that are present in Adventurers League games) that can let a Longbow based archer make a bonus action attack like a Hand Crossbow based Crossbow Expert can?
Best Answer
Yes, through use of the Swift Quiver spell
Swift Quiver can be found on PHB pg. 279.
As a level 17 Ranger, you get access to the Swift Quiver spell which allows you to use your bonus action to make TWO attacks with your bow, however the ammunition from the quiver is non-magical.
So, anything that grants you access to this spell will allow you to use your bonus action to make attacks with your longbow. And this is not limited to Ranger alone.
For example: Bard, level 10 feature Magical Secrets (PHB pg. 54) let's you take 2 spells from ANY class and make them Bard spells. Since Bards have full caster progression this means you can select this spell since it's a level 5 transmutation. As a bonus, if you go College of Valor, you also get the Extra Attack feature.
This means you can make two longbow attacks with your attack action, and two additional attacks with your bonus action for as long as you maintain Swift Quiver.
When all is said and done, in my opinion, Bards are better Longbow Rangers in D&D 5e than the Ranger class is, at least prior to UA releases (which may make this statement untrue at some point).