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No best answer has yet been selected by crgb14. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.The only ones I've seen readily available which fit right into the top corner of a room are a range of tetrahedron speakers made by TOA, like this one: http://www.toa.de/en/PS/F-10B.html.
They're more designed for sound installation purposes, like shops and restaurants, than for home use.
I think maybe the reason there are so few is that from a technical point of view right in the very corner isn't the best place to put speakers - they should be a couple of feet out in each direction to avoid any weird interactions with the walls.