Depends on the type of programmers you want to hire.
You can hire freelancers on resources like Upwork, Toptal, Fiverr, Freelancer
In-house developers: Indeed, Glassdoor, LinkedIn, or Dice
Outsourcing companies: Clutch, GoodFirms, ITFirms
Perhaps this guide on where to find programmers will also help you: https://www.cleveroad.com/blog/find-programmers/