On his site Tomas Votruba has a post sharing one thing he thinks is holding back your company from doing well: not open sourcing code.

Do you want to hire developers? Do you want to hire those developers who help your company in the long term? Do you want to save money for random picks of HR agencies? Do you want to hire developers who already know your code before even meeting you? Do you want to attract developers in the long term with zero investment?

Go Open-source!

He goes on to talk about some of his own experiences in the job interview process and how "old-school methods" aren't working as well as they used to. He then makes some suggestions about how to attract programmers "in a 2018 way". He uses a comparison between the traditional hiring process and a newer one ("open hiring"). He makes the suggestion of, when looking to fill a role, going to the contributors list of your or other popular packages and see who has contributed and reach out to them first. This allows you a preview into their skills and lets you evaluate it (and other contributions) against your needs for the role.