BGS #115
I dont remember if the bits are 6.0 or 6.5mm long, but they look like a box of tic-tacs. Seriously tiny, they have a groove with a spring collar to keep them in the ratchet, and the socket/anvil for them goes right through the ratchet and is peened on one side to keep the bit in. The ratchet is made from 2 stamped very thin plates with the ratchet wheel, spring and switch sandwiched in between. Kinda pricey. Ze Germans
SK11 SRD-210
A slightly thicker version of the BGS, I dont have one but I'd assume it's reasonably high quality. Good selection of 12mm long bits but it looks like there are only flat and Phillips tiny tiny ones purpose built for that ratchet, way cheaper than BGS but that could just be a regional (NA) thing
SK11 SRD-220
Regular looking, cast body ratchet but 3 inches long and comes with 12mm bits, they have a good selection of other 12mm bits too. Has a thick rubber grip probably to make up for the tiny grabbable area. The action is extremely light and it has a big, very useable thumbwheel. Everything on it looks and works beautifully. The reversing switch is absolutely miniscule and has cast details that would make a Gundam jealous, really nice tool, not too pricey.
Or if you cant get a bit that short in, you could just put a ¼ box wrench on a regular bit and back it up with a prybar on the end if it wants to slip