Contextual Teaching/ Vocabulary Links

I have a friend (not a client yet) who is interested in the concept of SEO, but he is quite worried about link building. He is more interested in finding niche blogs that exist and already have trust etc. that could really boost his site.

His niche is teaching / vocabulary and his site is somewhat successful already. He has over 6000 pages indexed with Google and many of them on page 1 (without any off-site SEO). It is all organic.

Any places to get such specific, contextualized links?

Maybe you can start looking for these contextual links by searching google by a footprint(like site:worpress.com) + "vocabulary" and then make comments/posts on these sites found by these footprints. Say thanks if you like my solution