Any standard square taper (for instance) crank will work on any standard square taper bb OF APPROPRIATE LENGTH (Campy square taper is not standard.). So if your bb spindle is long enough for a triple you can put a mtb crank on it. I got a nice single bmx crank of appropriate length on ebay for a reasonable price. If you want to use your double road crank with a single chainring and clean up the look you can put a cyclocross chainguard ring on the outer position. I keep thinking about doing this, but I just haven't decided to spend the money for cosmetics. If you feel comfortable working metal and have the inclination you could probably take a worn out 52T chainring and cut it down to appropriate diameter for use as a chainguard with a smaller chainwheel. It just needs to be a few millimeters larger than the chainring.
Regards,
Raymond