The best way to do it is to enter the name of the product on a search engine and perform a phrase match search. The product with more sponsored links is the right one. The reason is simple; if so many people are spending their money to promote a product it's because they are getting a big revenue in return.
A lot of merchants don’t join a network. This can be because they think the networks are too expensive, they want to have more control over who sells their product or they have developed their own affiliate software.
The simplest way to find new affiliate programs is simply via search engines, like - Google (type in ‘your topic affiliate program’) but it can also be worth spending a little time digging around in some of the larger affiliate networks like Clickbank, Linkshare, Commission Junction or to even look in Google AdSense’s Referral program (where there are new options being added all the time).
Start Your Search
This sounds a bit backwards but actually makes a lot of sense. Start with your own goals and the types of affiliate sites you operate or plan to operate. If you're going to target certain regions or countries of the world, you'll need to limit your search to affiliate programs with a strong roster of affiliate programs that operate or are well-known in that area. If you plan on building affiliate websites for online poker and casino sites, don't sign up with an affiliate network that only has one online gaming affiliate program available.