How should I search for prospective businesses for affiliate marketing?
Merchants (the seller) and affiliates (sites that promote the merchants) typically come together through affiliate networks. These are clearing houses that match affiliates and merchants, provide third party tracking and may manage the payments.
There are several reputable networks, including:
As an affiliate, you'll find tools for ranking merchants, etc.
As a merchant, these give you access to a vast range of potential affiliates.