In many respects, the way a specialist IT recruitment firm will go about the business of securing the right talent will not differ greatly from mainstream recruitment agencies. They will use job boards and social media and a range of industry standard tools.
It is what happens beyond that 'industry standard' that gives most specialist IT recruiters the edge.
IT and IT Project Management are niche endeavours. If you were the CIO of a bus company would you expect the same recruiter you use to find bus drivers to search...