4Seven's sells them in sets of 3...I highly recommend this. my first purchase was a set of parrallel and a set of right-angled two fishblocks (cyclobock and lockblock?)
Where can you mount it? depends on your cycling. For urban riding you'll be fine on the handle bars. Anything off-road, IMHO, the way to mount this is to the main spar (torch head at the forks, tailcap towards the seat post). I've found even my MG PLI too heavy for aggressive cycling (as in, the light has too much mass and moves around) so no way a tk40 can do a handlebar mount. Mounting to the frame is awesome, p7 I put there never wobbles.