Marketing_Guy - 12:17 pm on Jan 19, 2012 (gmt 0)
Not really used freelancers on that scale - always had a few contacts already available for the one off jobs we've been doing. Most the freelance job boards have a good selection of freelancers though, but it might be a case of trial and error to find a few that work well for you.
If you are focusing on one particular market quite heavily (for a few clients), then it might be worthwhile hiring someone full time to work from your offices. It'll give you greater control over the strategy, a quicker turnaround and probably more cost effective.