When you say "good" affiliates I'm assuming you have some affiliates now but the traffic & conversion is low. You could proactively find websites that represent your niche and email the webmaster about your program.
Many merchants have nice features to their affiliate programs that act as incentives for affiliates to choose them over other similar merchants.
As an affiliate here are some things that attract me to a merchant's product(s):
I agree with the comments made by DeepInTheCode, and would add a couple more:
1) Prompt, efficient support 2) For a standalone merchant, a relatively low payment threshold - eg payment is made to the affiliate once commissions reach $25/£25 rather than having to accumulate $100/£100 or more