why not by a dc to ac converter then step it down to 24v. This could be done for around 100.00 or so depending on how many lights, and how much the converter is. They have them every where now. And your local radio shack will have a step down transformer/power supply.
This set up will be easier and cheaper than adding another alternator. It is your choice though.
This set up will be easier and cheaper than adding another alternator. It is your choice though.