You could probably get away with 30 amp fuses if your gains are set low...I wouldnt go over...i went to auto zone, and kragen and i looked in the internet but i cant find none all i can find are 30A fuses.
Just keep your gains low...if your fuses blew that means that either sometihing is shorting your amp, you have a huge voltage spike, or your gains were set too high. Its most likely the latter...thats what i was thinking. i was looking at the new d3 800.1 and they use 30A fuses so it might work for the 600.1