You are right, the problem for me is that I'm not a programmer though I work in IT business.
I'd think that calendar data even in the worst case is relatively small, so using sql to locate items matching a search string could (at least) to be a starting point.
What would be neat is that the search would list results categorized by context (like description, birthday, event name etc.) sorted by date, for example.
Otherwise we'd need a separate search index that should be kept in sync with changes in calendar DB.