Google-search – What happened to the Google Calculator? Does it still exists

It had been gone in redesign few months before you asked this question and most probably you had enough time to assure yourself it won't return ever.

One mitigation would be adding those keywords from topic to search query text. The other could be limiting search down to particular publishing site with site:example.com/path stem, if you know that info in advance.

Update

Observed on 2013-06-13: the calculator no longer requires JavaScript and more importantly copy-pasting the result now works again! (This works both with and without JavaScript from google.com blocked.)

Google Calculator now requires JavaScript. In particular, JavaScript must be allowed from google.com.

In the case of Firefox and NoScript, google.com may be blocked. To use Google Calculator, set NoScript to allow JavaScript from google.com (permanently or temporarily). Unfortunately, copy-pasting the result from this window does not work. Thanks, Google, for breaking the ability to use the clipboard for getting the result.

In the case of Opera, allow JavaScript in site preferences.