On my current position as HR Business Partner in a large multinational IT company I have been several times responsible with the recruitment of specialized candidates. Shortly after I was hired they asked me to find a few Linux guys that also spoke English plus French/Italian. Trust me this is not that easy to find.
After posting the ads several times on the best paid job portals and waiting for the candidates to apply I have realized that they weren't going to come to us that easily. I have realized that good IT guys are also a bit weird (please forgive me, guys, but like all geniuses, IT ones are out of the ordinary too) and are not actually open to new positions once they are engaged in a project unless you go to them and convince them that what you can offer is better.
I was desperate for CVs and at that moment I have discovered the magic of LinkedIn. I had very low knowledge of Linux, but I managed to find my good candidates. How can you do it and more than that - for free? LinkedIn offers great possibilities for job posting and searching, but as all large and famous portals, they cost a LOT. So, how can you do it for free?
First of all, register with LinkedIn. Fill in your profile as accurate as you can. A sloppy profile will always be rejected by groups and partners. Be professional and spend the necessary amount of time to fill in your information. It will be worth your time, trust me.
After you have created your profile (don't forget your picture to build your trust) search for groups. I have searched during my recruitment projects for keywords like "Linux", "SAP", "French speakers" or "Francais" for groups in French, or for various groups where IT recruiters met and posted ads. When you have a group you are interested in, apply to become member unless it is an open group where you can post ads and comments without joining. Don't give up if some groups don't accept you. Headhunters may be considered spammers sometimes and some groups focused on technical issues only may not want you.
When you get accepted - and I got accepted in most groups I applied for - post a job ad in the Jobs section or in the Discussions section if you ask for advice or are looking for connections or more than just CVs. All the jobs and discussions are sent periodically (daily or weekly) to all the members of the group on their email (unless they have unsubscribed from group news). The more groups you join, the better chances you have to reach a larger audience. Also select the most active groups or those with more members - LinkedIn offers you this information when you search for groups.
I am allowed to be member of maximum 50 groups, but that's OK as you can step out of a group and join another or rejoin the first one again anytime.
Good luck with the recruitment of difficult positions and please remember you can come back to me with questions anytime.