This grower is sure of this plant identification.
I have a couple of these available in 3" plastic pots
Agave Triangularis (Triangle Agave). The leaves of the Triangle Agave are olive green, dagger-shaped and 45-60 cm long, with a pale midrib, small marginal teeth and a 2cm terminal spine. They flower infrequently, but when this occurs the flower is yellow.
Architectural, drought-sensitive planting, evergreen