Where can you get a 5S5A125V fuse for an RCA 300 watt stereo?

You could try to get a pack of busman fuses. They fit perfectly and have the same exact rating. But I would say dont bother. I have the same system and I replaced the fuse 3 times and as soon as I plug it in the fuse blows. I think the transformer might be bad or i have a short somewhere in the amp.