Prior to that group, they had an online community for teachers looking for lesson plans. That probably sounds pretty random, but it's crazy the type of communities you can build and rally people around. If it's something that you're passionate about yourself and you want to connect with others that have that same passion, then an online community is something you should definitely consider.
I would have one partner create a separate page/contact form specifically for the advertiser – so only people who see that contact form are people who were referred to by the advertiser. The advertiser would use that page as their outbound link. I know you can track outbound clicks in Google Analytics events and Contact Form conversions (usually through most contact form plugins) but that is the best way I think. Never done it, but this is how I see most affiliate programs like that work.
Fiverr: Israeli-based Fivver was started in 2010 by Shal Wininger and Micha Kaufam. It's a great resource for selling just about any service online. You can offer gigs as low as $5 but also get paid much more for upgrades and add-ons. There are plenty of providers earning 6 figures on Fiverr so it's definitely a worthwhile cause for generating a healthy income. Just ensure that you provide some serious value.