Kazuo Koike and Goseki Kojima historical manga is quite good, such as Shingen Takeda, the Tiger of Kai, or with a touch of fantasy such as the Legend of Kujaku, that inspired both Jojo's Bizarre Adventure part one and Berserk. The original trilogy of Jojo is something I recommend, but since you said no mainstream... Leiji Matsumoto drew great ships and compelling stories you must have already read (Galaxy Express 999, Queen Emeraldas, the diferent series of Captain Harlock). There's more manga to read from that period, but these are a good start and available.