That is an awesome question. I've had success in doing the Boolean search and then contacting everyone I can in that specific skill set. Sometimes it's just a numbers game... the more people you contact - the more chances you have of a few people getting back to you. I've noticed that a lot of people don't change the dates their jobs when they are unemployed (at least not right away). Good luck!
Try adding "seeking" or "available" to your search. You'll find a few that use that indicator. (You'll also have to sort through quite a few recruiters "seeking top talent" or that have "awesome opportunities available" and such, but you'll get there...)
Search for "looking for a new opportunity" or variations of that (searching/seeking | position/challenge etc.) - they often put it into the professional headline. Of course, you also need to filter for position/industry.
Try going to recruitingbar.com it is our free boolean search toolbar created by sourcer Ryan Leary. It has the searches built in.
Nick - Welcome aboard. There are a few key ways to achieve this. It depends on the version of LinkedIn you are using as well. Assuming you are using the basic account, you can do the following:
1. Try search only for contacts listed as open to career opportunities.
2. Remember that LinkedIn has no limit on the # of terms searched: Add this phrase into your search: ("looking for" OR "currently looking" OR "new career" OR "new job")
If you are on the CAP or RPS service you can use various filters to help narrow the list.
Download the Recruiting Bar at http://www.RecruitingBar.com