Its not about contributing to open source, its about demonstrating that you can deliver stuff. Open source is a way to do it, but not the only way.

I dont have a github, but Ive only been rejected one time, which was for a crappy job anyways. In intervews I talk about extremely technical things I worked on during my times at other companies, and its usually at a level above what the interviewer understands (for example, impelenting a library that decodes fax data, made harder by ancient documentation) so I look really good.