Single-Phase to Three Phase Cycloconverter
If there are single-phase-to-single-phase cyclo-converters then using three together (control phased at 120 degrees) will produce a 3 phase device. The IEEE reports that they have been studied here.

The main difficulty is that with a single phase input (at say 50Hz) you can't create a 3 ph output at 50Hz - this means that they are likely to have applications in specialist slow speed motors areas and this may be a small area of the market and hard to find data on.