You can setup an affiliate network of your own for very little upfront cost using http://www.hasoffers.com I think they are one of the best 3rd party affiliate platforms. PLEASE NOTE: you will need a coder to integrate with your existing site / products.
Once you have your affiliate system setup you obviously need to recruit affiliates. You can find new affiliates by:
1. Partnering with existing networks who can run your offer (this can be done w/ hasoffers system very easily)
2. Post in the lounge or appropriate area on niche related forums. Kindly mention that you are looking for affiliates to promote your product, describe the compensation structure, and other relavent details.
3. Buy ads on marketing forums (such as BHW) where you can find marketers looking to promote hot new products