Hentai Conventions?

Do they have these?

I frequent normal anime conventions and they got their little hentai corner, but is there anything on a bigger scale?

Exclusively for Hentai? No. It's always been a subculture to anime/manga culture. The closest you'll get to that is comiket or other dojinshi events in Japan.

http://www.yaoicon.com/about.php
Project h had hentaicon but they never redid it past 2014.

Yaoi con is my life's dream and goal. Once I have fulfilled it I will turn into a rainbow butterfly and soar into the atmosphere, becoming one with earth and our solar system.