I don't know where you can find one, but I can tell you about the one I had for a while.
It was a 17 gallon LONG, measurements: 28" x 12" x 12". Basically the footprint of a 29 gallon, but 1/2 the height.
I made 5 home-made acrylic dividers, using plexiglass, a jigsaw and a 3/16" variable-speed drill. I measured, then cut a cardboard template first to make it fit around the sides, botton and within 3/16" of the hood/cover. I then traced the template, cut the 5 plexiglass sheets with the jig-saw, then drilled about 100 @ 3/16" holes in them (clamped together to make it even and faster).
I made the dividers friction-fit, so that the tops were tight against the bottom of the top tank trim. I just tilted them in and out at an angle. I made-up 6 divided spaces (about 2.8 gallons each). Put rocks and live plants to make it look more natural. (I would use sand next time with some driftwood and java moss)
I put a heater on one end, and a submersible powerhead with quick filter in the other end. I then ran some PVC tubing from the powerhead outlet, up into the feeder slot of the hood, and over to the opposite end of the tank. That way, the water would pump from one end to the other, and draw the heat accross all the cambers in a slow, continuous fashion.
It worked REALLY well. However, because I was breeding and always changing fish, when one got sick, they ALL got sick. So, I changed back to big bowls with lids.
So... some tips from a guy who's done it.
1) Make sure the dividers go all the way up to the top of the hood and no gaps. These guys are jumpers and will go after each other by jumping over any gaps in the dividers.
2) If you can, maybe add a UV sterilizer lamp to the tubing to help keep it cleaner.
3) Make your own divider and take your time drilling the wholes. Plexi-glass cracks easily if you force the drill or jig-saw to fast.
Hope this helps.
) currently being offered in most chain and LFS's. I don't want the height or width of a traditional 20 long, just something short and long. 
