We have very few items for AD assassins. Duskblade, Ghostblade... uh... Edge of Night and Black Cleaver? They could use another item. Sword of the Divine is a burst item in design - you activate it and it gives you 3 quick and devastating basic attacks. Like Hail of Blades but with crits. With some tweaks to the design, it would be a nice option.
* 10-20 Lethality
* 50 AD
* 5% Movement speed
**Active:** Your next 2 basic attacks have 100% increased attack speed and deal X bonus physical damage. 40 seconds cooldown.
The active would deal more total damage than Duskblade's proc, but it'd be fair since it takes more time to deliver the damage and can't be reset by going into stealth. I changed it from crits to flat physical damage because I want this item to synergize with lethality, not Infinity Edge. I also took away the passive attack speed because that's not really a desirable stat on these champions.