iTunes used to have a Power Search feature, but it has been removed from the iTunes app (though you can still access it this way). Power searching is really useful when you want to home in on something in the iTunes Store, App Store, or Mac App Store.
In the absence of a real power search, you can search another way: with Google. A Google search works because Apple has Web pages for all its iTunes Store content. With Google, you can search for more specific keywords and use quotes to search for specific phrases.
Perform a search like this (replace the terms in brackets with the item you’re searching for):
[artist] [title] site:itunes.apple.com
You can add other keywords, such as the name of a record label. So, if you wanted to search for Steve Reich’s album Music for 18 Musicians on the ECM label, you could run the following search:
"steve reich" "music for 18 musicians" ECM site:itunes.apple.com
(The quotes narrow the search to the exact phrases that are quoted.)
Google returns a lot of results, the first of which should be the album you’re looking for. You’ll see results from several countries, so look at the URL: after itunes.apple.com, if you see /us/, that is a U.S. store page; /gb/ is for the UK; /de/ for Germany, and so on.
Click a link in your search results to open its iTunes Store Web page, complete with a View in iTunes button that you can click to open that “page” in the iTunes Store.
You can also use the same technique to search for apps, using keywords, specific app names, and more.