You don't need to have maxed the digging score to find the item. It just makes it easier. :D
As for the quests, there is no list anywhere which says all the ingredients needed for each quest, because a lot of it is random/variable!
There is a list of all the quests (or was, I do not know if it is 100% current), and it says the things that are known about ingredients listed (For instance: 1 Angel Tear, 1 Mermaid Tear, 6-15 random rares, 20-80 random average, 100-300 random prevalents. Or whatever).
But it can't give you exact amounts.
I can try and find it somewhere...
The nice thing is, quests are not limited-time. So if you don't have the stuff right away, no worries! Just keep digging and trading, the quest will wait for you.
