What I'm reading into the question is what to do with the stiff green tops. For stocks you can use them as the structure for a bouquet garnie. A couple of layers of green leaves, and in the middle, whole branches of parsley and thyme. Tie that all together with kitchen twine.
Flavorwise, the closest thing would be shallot or green onion or a combination of the two.

I have never understood why folks discard all that good stuff. When I haven't been able us use all the green stuff in a timely fashion, I have diced it finely and dried it. Then I store it in a jar by the stove and when I need a little oniony flavor in my dish, I will throw in some dried leeks.

I do the same thing with my Egyptian Walking onion tops. Nom Nom!

I struggle to find leeks that are grown properly . . . they should have more white bit than green bit. It is laziness on the part of the farmers who do not constantly mound soil around the growing leek to force the white part to dominate the green part. Complain to your local green grocer to buy better quality. I have and it can make a difference.

Trader Joe's is selling frozen chopped leeks from Belgium. Great taste and no waste.

Also great to save for veg stock.

Well, I just walked past leek displays at two different groceries and both had gray, dry, fuzzy/dusty outer leaves and only 3"-4" of usable white-greenish white for almost $3. I bought two bunches of green onions @ $.89 each.