I agree.
>>>> I used to make custom WordPress websites for family and friends
Is any of them still active? Can you make a new one as sample to build a portfolio?
>>> The internet is full of open source projects, starving for motivated contributors - and they also make a great portfolio
My recomendaion is to contribute to projects you already use, so you understand the use case. It may be helpful to explain to a potential employer something like:
fake quote> In my previous job I used this library in WP but it has an anoying bug/typo. So I fixed it and it got merged in the main project.
Start with easy stuff like typos/bugs, and later try to add features once you are sure the mantainer will apreciate it.
Don't expect to get paid for working in the open source projects, take it as a hobby and as possible portfolio, not as a income source.
Also, there are three official post in HN about jobs. They will be posted automatically on thursday. Take a look in case you find something useful and you also may post in the correct thread. You can peek the last month edition in https://news.ycombinator.com/submitted?id=whoishiring but they are read only now.