The Lyra Helicon mono is regarded very highly by a lot of people, and I've heard that the Titan is available in mono on special order.
At more modest cost are the Grados, all wood bodied versions of which can be wired for mono on special order plus their mono MC+ and ME+ cartridges.
At more modest cost are the Grados, all wood bodied versions of which can be wired for mono on special order plus their mono MC+ and ME+ cartridges.