I'm not an expert on tube power amps, but I would think that heat would be a big problem for a 1RU amp, which would explain why I can't find any. There's the Mesa 2:50 (which is 2RU), the Carvin TS100 (which is 2RU), or the Matrix GT800/GT100 (which is solid-state), and several others. As far as I can tell, you'll have to compromise on something.
Edit: nice find dpavel! Just got to wait for it to come out.