There's a MacTech tutorial here which includes a search example: http://www.mactech.com/articles/mactech/Vol.21/21.11/ScriptingiCal/index.html
Here's a working example of how you might find calendar events that match a search criterion:
tell application "iCal"
tell calendar "Domestic"
set theEventList to every event whose summary contains "Recycling"
end tell
set theEvent to first item of theEventList
return summary of theEvent
end tell
This example works for me. It finds all events in my "Domestic" calendar which contain the term "Recycling" and then returns the summary of the first one in this list.