I have a bunch of landmarks that don't appear in my inventory.

[Berry Cremorne]

Basically in my map view I have a load of landmarks that pop up, but when I go to my inventory none of them show up. They're mostly from stores etc etc but I have no idea how to find them (yes I've tried searching) but alas, no result.

[Alwin Alcott]

those are spreaded in all folders that contain the items you bought at those places.

You can easely sort them with using the custom search in the inventory, it will only show landmarks, you can drag them to the LM folder and delete the doubles.

Than you will see all on the same place

[Lindal Kidd]

When you Search your inventory, use a filter, and limit your search to Landmarks.  This should make them easier to find.  Then you can drag them into your Landmarks folder and organize them into subfolders.

If by your "map view" you mean the little globe button and teleport history, those are places you've been.  You can use that history to return to those places, then if you want a permanent landmark, click World/Landmark This Place.