How can I develop a list of niche related directories?

How can I develop a list of niche related directories?

A few years ago I spent a lot of time in building free directory lists from different niches and topics so that I could submit my client's websites into directories related to their content and overall website idea.

Now I think I should do the same for some local clients. Problems are there are no more updated directory lists out there! SEOs used to share these lists on forums and special blogs, but most of those forums are dead and the blog posts are inactive, with directory lists being not relevant anymore.

How do I get such lists again? The directories need to be free to publish, I'm not willing to pay for those links, any special tools to scan for such websites that are still active?

Thanks.