I have easynews setup as the server but I don't see where I can add a Easynews tab for search results from them.
Unless something has changed that I'm unaware of, the only search tabs you can use are the ones RDL has programmed support for. You can't randomly add search sources/tabs. This shouldn't be much of a problem in actual use, though. Just use one of the existing search engines such as binsearch.info.