London Taxi TX2 Alternator Upgrade

[FazB]

I've just bought a London taxi TX2 and put a sub and amp in, gonna be putting in rear speakers next month too as only front speakers for stereo at the moment.
Ive tried to look around and can't find any options for upgraded alternators... What options do I have? Can I fit another type in? Can I make the current one any better? Am I gonna regret this? (probably yes to the last)