Searching is already possible, but I notice that you cannot invoke the Find form from the Table Definition Editor. We'll fix this.
For example, if you view or edit a table, open a new SQL Window, invoke "Find", switch to the Table Definition Editor in the background and focus the column grid, you can now search.
I have added the "Copy to Excel" suggestion to the list of enhancement requests. You can already export to CSV and open in Excel of course, which is not as easy as a direct Copy to Excel.