There is a vendor on Ebay who regularly sell an 100amp Alt. the price varies from about $60 to $85. He has very good feedback. I purchased one but have yet to install it. It is in an identical ford case, you basically can not tell the difference by looks.
You can also have yours rebuilt to a 95 amp ouput. A reputable alternator shop can do this and the rebuild kit is available.
1966 Red Conv (200)
1966 White Pony Int.(289)A Code
1966 Coupe (289) C Code
MCA 36048