Directories can be very specific to the niche of interest. Spend a little time researching your top five competition. Find out what backlinks they have and where their customers hang out.
Personally I like to have a clear understanding of who and where my avatar is going on the internet.
Create a Google Sheet or a Excel Workbook and start a list of all the sites that have a meaningful link to your top competition.
This might help researching your competition, 5-free-online-backlink-checker-tools.html
Once you have this information you'll see it's a list of posts, directories and a lot of stuff you never heard of. Now you can create strategy for virtual networking and authority building.