The company's website touts the horn as being handmade, so I imagine a person could request water keys. I'm betting they could buy them from suppliers.
BTW, if you REALLY like that dark look, you can also get the look from Adams. They don't show a euphonium, but here is a flugel - click the image to expand it. (I personally like the look OK on flugel or tuba, but don't care for it on euphonium.)
Or here is a tuba that I like, which is a little less radical: