I recently finished the Nichijou anime and I noticed there are an OVA and specials (Nichijou: Tanken Nichijou no Machi). According to MyAnimeList, there are 14 episodes under this title as you can see in the link but I only can find 3 episodes. Can someone direct me to where to find all of the specials?
There's some confusion about what "Tanken Nichijou no Machi" is.
It is not the thing you've seen subtitles for. The things you've seen subtitled are a promotional video and some unaired next-episode previews. Typically, these things are not construed as "specials", but in this case, they've been incorrectly conflated with and mistaken for "Tanken Nichijou no Machi", which MAL thinks are specials.
"Tanken Nichijou no Machi" does not consist of a promotional video and some unaired next-episode previews. Rather, it is a series of ~10-minute live-action clips featuring the Nichijou cast and staff (mostly Shiraishi Minoru, really) doing things that have hardly anything to do with the actual show. Here is the first of them on YouTube (could go down at any time).
They're kind of interesting to watch, I guess, but again, they have absolutely nothing to do with Nichijou besides featuring the cast and staff from the show.
I suspect that MAL is the ultimate source of this misinformation. If somebody knows how to get an entry delisted from MAL, they should probably do that with "Tanken Nichijou no Machi".
Anyway, to answer your title question, I think there are 11 episodes of "Tanken Nichijou no Machi". YouTube appears to have episode 11, and the official website for the manga lists episode 11 being planned for inclusion in BD 13 (the last volume).
However, this is a little confusing, since BD 1 and BD 2 appear to include a thing called "Tanken Nichijou no Machi", which might be distinct from "Tanken Hakken Nichijou no Machi 1" on BD 3 (continuing through to BD 13, which lists "Tanken Hakken Nichijou no Machi 11"). So the answer might actually be 12 or 13? It almost certainly isn't 14, though.
There is something of a lack of information on the internet about Nichijou's BD content, because the discs had abysmal sales, owing to the large number of them (13 for 26 episodes; 11 or 12 is more common, I think) and the high cost of each individual volume.