You way use iTunes Search API to look up your and other apps on the App Store.
Docs: http://www.apple.com/itunes/affiliates/resources/documentation/itunes-store-web-service-search-api.html
Example: http://itunes.apple.com/search?media=software&country=us&term=raining%20weather
iTunes may return more then one result, but you can filter results by bundleId
.
trackViewUrl
will contain iTunes URL to your app. trackId
will contain app's ID.