Aside from making official accounts on the Fediverse, I think anons should try to promote boards for specific topics on platforms dedicated to the same topics. For example, the loli/shota boards could be shilled on ATF and baraag, /fur/ could be shilled on FA, /fast/ on Sonic forums, /hisparol/ on Hispachan (since that's where the board originally came from), /v/ and /vr/ on video game forums that aren't completely cancerous, etc.
Another idea I had was to use the board message sections to crosslink related boards. /b/ links to /c/ and /hebe/, /c/ links to various boards (including /vr/), and the loli-shota boards link to each other. This increases their visibility when one of the boards isn't visible in the top navbar.
Speaking of /interracial/, what are you going to do now that there are two boards for the same thing (3 if you count /2dblacked/)?