>>2876
>>2877
/cm/ is a good board (or at least is much better than the big boards), I lurk their shota general and a couple of other shota-centric threads. Sometimes an autist drops their spaghetti over something ridiculous (like the fact women browse that board or the obligatory "you're pedos" sperg), but on average things are quiet. The problem, however, is that mods are heavily against any forms of advertising, specially when is for other imageboards (the word 8chan has been marked as spam since the exodus to done 5 years ago). Direct advertising won't work there, so your best chance is to casually mention the site during a random conversation.
Another board with shota threads I browse from time to time is /vp/. They have threads and generals for pokeboys (with Allister being a popular one) and a sizeable part of the users are into lolis, so the rejection for a board like this one or /loli/ may be less harsh. Of course, since its a bigger board with more normalfags, trolls and moralfags there's a higher chance bad users crawl here and shit up /v/ since its the biggest board. Also mods still can ban you for advertising 8chan, although they usually don't lurk waifu/husbando threads and only respond to reports.
/v/ and /co/ have shota threads and general husbando threads from time to time, but the amount of cancer users there may be too high to promote the board (and as a consequence the site) without causing a bad effect.
>>2879
My biggest gripe with /b/ is that is full of legit newfags, normalfags and pedos. It has active threads every day, but the quality of the posts is godawful. Pics reposted again and again, low quality files clearly saved (or worse, screenshots) from Facebook and Pinterest, ugly uncanny 3D models, spam of all kinds, and the worst of all, retards talking about real children and using the words loli and shota to describe them. It would be easy to advertise /sm/ there since ad posts rarely are reported, but I don't think it's worth pandering to them. They're called the shithole of internet for a reason.
Outside of 4chan the biggest sites are ATF and baraag, but both require accounts to post. They could be good places to promote /sm/ (and the loli boards), but I'm not sure how this could be done.