The MDI menu is context sensitive - it's view specific, based on the View that currently has focus. When the Trend View has focus, what do you want it to find in the Trend View?
Even when the Search menu shows up, the Find dialog is specific to the current view.
Doc Editor, it finds elements in the doc view. XRef View, it finds elements in the XRef. Ladder View - finds elements or instructions in the code with a bunch of options.
Start Page, Dashboard - it's missing just like Trend View
Trend View - what command do you need in the missing Search menu?