Hi Swati-
If the LP is still in draft mode, it will not show in the smart list drop-down menu until it is approved or approved with draft. The other option is that the LP has been placed in an archived (inside Design Studio) folder, the LP exists inside a Program and you are trying to reference from a different program (local assets are truly local), the program that contains the localized LP has been put into an archived folder, or the LP exists in a different workspace that has not been shared out to your workspace.
Hope this helps.