Well done! She looks like a lovely car, and how rare to find a nice elderly R4 that's been looked after so well. Does she have a name?
I'm not helping much with the alternator. Why do you want one? French dynamos are much better than Lucas ones and they actually work a bit. I tested one recently and it was possible to operate both headlamps and the wipers continuously without the battery going flat.
There are several more efficient people on here who should be able to help with spares much better than me, though if you become desperate and are a man with spanner who will travel to remove alternators from cars of unknown origin I'm right here.