My workflows happen to use a number of TaskPaper files (different projects, different days), and whenever I start a new file, there are usually one or two existing @searches which I want to paste in from other TaskPaper files.
Here is a draft macro which just gathers existing @searches from:
Any TaskPaper files which are open at the moment
One or more default TaskPaper files which you can list in the macro.
It offers a menu (without duplicates) from which you can choose which @searches you want to paste into the active document.
You could also do something like this with TaskPaperRuby.
As a simple example, to grab all @search items from a certain “old” file, and append them to a “new” file gathered into a project called “Searches”, this would do it: