I know River Service in Japan was selling new replacement psu's for sega cabs, I actually bought one a long time ago for my Blast City, but I can't find any info about it on their site about it anymore. It appears they switched their focus to displays.
so, I'll tell you a little story about my Astro City. I got this cab from ken@gameroom in fall of 2011. It has a happ power supply in it and I've never had any power issues with it whatsoever in the 4 years I've had it. It's not pretty on the inside, but it gets the job done. He wired up three standard happ style buttons for test, service, and degauss. I just took a look on ebay and saw some for less than $30 shipped! As far as setting it up, I can't help you any further cuz I'm a totaly friggin noob with that stuff
hope this helps buddy