I just upgraded a 3x9 XTR MTB groupset to 2x10 just by swapping in a set of road flat bar trigger shifters, 10 speed cog and chain. I got the cheaper Tiagra which work great but they also have a similar Ultegra set that can be found as cheap as mid $60s. So they are out there. Maybe not for 3x7 though but if you are going to upgrade might as well get away from that anyways. I guess the short of it is you can easily get some flat bar Shimano shifters and the use standard road derailleurs or you could just get a MTB groupset. If your looking at second hand then any of those can be had pretty cheap.