Out of those "find me X number of these widgets" quests, which are you having the hardest time with?
For me it the Jazbay's, I have 6 of 20 at level 50. At this rate i'll need to reach level 130 before I get them all. I think next would be the Stones of Barenziah, i have 19 so far.
I usally don't activly look for these type things, just play the game and figure they will turn up. I also don't buy any that vendors may have.

Lots of Jazbays can be found around the area where all the hot springs & mammoths are. There are also lot of them in North & South Skybound watch. As for Stones of Barenziah, it would definitely be the hardest and the most time consuming to find.

Ingun Black-Briar's ingredients.

Seconding the Stones of Barenziah. No clues, no hints, nothing.

One thing I learned about the Stones is NOT to let Vex take a look at them, until I have them all, lol.





(um, because otherwise they separate inside your inventory)

Fetch me 20 jazbays er no how about fetch um yourself Im the dragonborn not a gofa.

Farengar Secret-Fire would disagree with you.

I'd say for me it's the Stones of Barenziah and the 10 Firesalts. Not a lot of Daedra around this time...

When I am given a quest for ingredients that I do not have yet, because the ingredient (almost always) becomes nonexixstent in all of the vendors inventories

Get her to value them after youve found 23. if you find all 24 before seeing her, the quest will bug out.