Is there an affiliate network like CJ or LinkShare, but just for SaaS applications?
There are only a handful of SaaS startups utilizing affiliate marketing as a way to grow their customer base.
After checking every affiliate network under the sun, I've come to the conclusion that either SaaS founders have no idea how to use affiliate marketing as a channel, or they've used it and considered it not effective.
As you mentioned, the SaaS companies that do use affiliate marketing as a channel are spread amongst the current top networks. Some have their own in-house affiliate program (e.g. Shopify).
There isn't yet an affiliate network that caters to just SaaS products. The closest thing would be Clickbank, which focuses on digital products (but it's usually ebooks and other informational products on there).
The reason why there are fewer SaaS companies using affiliate marketing:
That being said, every startup should try it out as a marketing channel to see if it works for them (and worth spending resources on). Instead of targeting every affiliate on the popular networks, a better approach would be fostering a relationship with relevant blogs as a way to recruit affiliates.
Most of the affiliates on the popular networks (CJ, LinkShare, Shareasale) are coupon sites. Not exactly the right audience for a SaaS product.