Try automationdirect.com They used to have one, don't know if they still do. Several years back they used to sponsor a NASCAR race car in that drek that passes for racing in the US. IIRC they used a PLC in the car. I can't imagine for what, except advertising.
You may want to consider an embedded PLC. In this case we distribute the FMD88-10 from Triangle Research. The operating voltage range is 12 - 24 VDC.
The outputs are transistor, not relay and are not bound by the coil voltage of the board relay. So you will have the ability to operate in the 12 to 14 volt typical range. The variance is +/- 5%
More information can be viewed through the following link: