I find
https://eq.magelo.com/ to be a fairly good source on what drops which items and how frequently.
Obviously, as their item collector wasn't a thing when people were farming Velious (and p99 doesn't always match up to live) you can't trust the information entirely, but it is a good starting point.
e.g. for Flawless Diamonds:
https://eq.magelo.com/item/25814/Flawless-Diamond