Well, such comics could have groundbreaking visuals, characters that become cultural icons, and maybe they were the first of their kind to introduce a new style or concept. Also, if they have autographs or limited editions, that could add to their value.
You might be able to find them on some less official manga sharing websites, but keep in mind that accessing such content might be against the law and could lead to issues.
MT hentai comics are known for their sexually explicit imagery and often push the boundaries of conventional comic themes. They may explore various fetishes and unconventional relationships.