Where can I get 24 volt fuses?

Electricity is funny stuff described by Volts, Amps, Ohms and the like.
We don't describe fuses by their Volt value we describe them by their Amp value. 
So any 12 volt fuses, fuse holders, cable, crimp fixtures will work quite happily at 24 volts.  
​Try not to use 240 volt cable or switches at 12 volt as they may not be up to the job.