Where can I watch Hentai Ouji to Warawanai Neko.: Henneko BBS?
Hentai Ouji to Warawanai Neko is licenced by Sentai Filmworks according wikipedia : https://en.wikipedia.org/wiki/The_%22Hentai%22_Prince_and_the_Stony_Cat.

If you go on the official website of Sentai Filmworks you will find the blu-ray here : https://shop.sentaifilmworks.com/products/the-hentai-prince-the-stony-cat-complete-collection

It is written :


  Extras: Clean Opening Animation; Clean Closing Animation; BBS Shorts
  (x12)


The BBS shorts are included. So you just have to buy the blu-ray.