I met someone at Whitby Folk Week yesterday who has a Tombo S50 slidless Chromatic harmonica. He let me have a quick blow and it was interesting. I've found more info on Pat Missin's site.
I found Amazon UK sell them through a third party seller and they were pretty cheap. The basic version was £27 and the violin scale (equivalent of a 14 hole) was £32 so I've ordered a violin scale one. It's coming from Japan so I won't get it till mid September but I'll keep you posted when it arrives.
There will obviously be a learning curve as it will require a different technique but it wasn't too difficult to play each "side" of the instrument separately.
If they had the notes laid out like a piano, it would probably be easier to play, (but I don't think they do).
Yes, the fact that each reed has its own chamber means no pesky valves.
(I've had some stuff come from China, & it arrived in 3 weeks, hopefully you won't have to wait too long.)