I know NOS makes it, I think ZEX makes it, you really don't need major modifications for a 50 shot, the stock rail and injectors are fine, if anything, get a pressure regulator and maybe a fuel pump, then you'll be ready for boost later.

NOS isn't as cheap as you might think though. Yeah the kit is only 500-600, but the Nitrous is not cheap. Are you ready to spend 40-50 a week on refills?