Where to find affiliates to join my newly created program?

I can't comment on the affiliate program, but Niceboard is an interesting idea. I use to be in the job board industry and haven't seen this before outside of ATS. There are so many job boards popping up daily - just search for remote jobs on HackerNews and you'll see a dozen new ones in the past few months. I can imagine a lot of these companies should use Niceboard because the interface is a lot "nicer" that most hacked together. Also, if you're a midsized company Niceboard is a good way to display jobs, but the trick is differentiating from the ATS systems like Lever.co or Greenhouse offer job management with boards...but they aren't great.

A few thought:

• Job sourcing. If I don't have my own jobs to post, would be awesome to have a source (for an extra fee) to draw from.
• If I do have my own jobs, I need a way to get the jobs into Niceboard. Thus an API or at least he ability to upload from an excel file.
• Another angle is have integrations with the ATS systems. ATS have the jobs and job management, but their candidate-facing job board isn't great. Let Niceboard be that beautiful candidate facing interface.
• Your favicon is missing.

Nice - I can be your affiliate ;)

Any tips on where to find people to join the program? I think the commission we're offering is pretty generous at 50% and could entice digital marketers if they only knew about it.

That depends on your target market. Is it digital marketers? Your landing page says it's for "publishers, businesses, and associations" and "employers and job seekers". Maybe drill down on one of these groups to something less generic and shoot your shot with them about your affiliate program.