If you have good mechanical skills and soldering skills, a mono-dock can be converted to a stereo dock.
Involves drilling 2 holes on each side of a mono-dock case (after disassembling it), removing 2 (or 4?) zero-ohm jumper resistors and installing 2 Neutric 1/4" jacks.
I did it with my mono-dock about 1 year ago. Drilling the holes is the hardest part - maybe a hacksaw and round file could be used as well.
Or for a little more money (less effort) - buy a used stereo dock from musicgoround, Guitar Center, Sam Ash, etc.