What is a pink and French backfill?

What is a good source for for CPC or CPA ads that can be used to backfill a growing online advertisement inventory as it is built up?

• I'm in the early stages of building a CPC and CPA display ad network (we're probably 4-6 months from launch).  Our model is to have direct relationships both with advertisers and publishers, reducing the "middle-man" cut as much as possible, and taking a comparatively modest cut of the revenue for ourselves. We already have agreements from several large publishers with global reach to test our network when we launch, together those publishers have thousands of impressions per second.  Consequently, I'm not so worried about the publisher side because if we can deliver the eCPMs, we'll get more publishers than we know what to do with. The most novel aspect of this (which I can't describe in too much depth) is that we make it easy for a large class of advertisers (representing over $25Bn in sales in 2009) to do CPA advertising. Unfortunately we have the chicken-and-egg problem to deal with, and so I must look for an alternative source of CPA advertising inventory while we work on building up our direct advertiser relationships. So the question is: what is a good source for CPC or CPA ads that we can use to backfill our own ad inventory as we build it up?

• Answer:

  On LinkedIn you can find small ad agencies giving out some of their inventories.