High Output Alternator for Custom Stereo?

Hi all, I'm getting a little ahead of myself as I'm nowhere near the point of installing a custom system into my 68 Chrysler. I would however like to have a good plan for when the time comes! I saw a video on YouTube (I'll attach the link below) of an awesome 1968 Chrysler 300 with a killer custom sound system. They mentioned using a Singer 300A alternator. I have never had luck finding such a high amp alternator for our cars. Do any of you have a custom sound system, and if so what...

High Output Alternator for Custom Stereo?