Don't forget Amphion, although there's not much 'horn loading' with their shallow waveguide. Also there was SP Tech now Aether Audio, although it looks like that company is about to go under for good. There's Geddes which makes a few designs using pro sound woofers and compression drivers in horns. Technically even KEF co-axials would count as a waveguide with modest horn loading.
And although they're both large, we (Vapor Audio) made 2 stand mount speakers with waveguide/horns, the Arcus and Aurora.
And although they're both large, we (Vapor Audio) made 2 stand mount speakers with waveguide/horns, the Arcus and Aurora.