David, Try these:
https://www.dataphone.se/~fixer/info.htm
https://www.minimania.com/MM/MINI___A_BRIEF_GLOBAL_HISTORY_OF_THE_WORLD_S_MOST_LOVED_CAR_.htm
https://www.minimania.com/Article_List.cfm
In the U.S., any Mini 25 years or older is legal. In Canada, I think the limit is 15 years. For better or worse, most customs inspectors can't tell a '76 from a '96, so there are a lot of newer cars around. Most carry the VIN of an older car that came to an untimely end. Personally, I'm not enough of a gambler to take a chance on a newer (or re-vinned) car. Although there were a few significant changes (hydrolastic suspension, transmission changes, fuel injection, etc.) the basic car remained much the same from 1959 to 2000. With tons of parts available, you can build or find nearly anthing you want. If you're going for an authentic restoration, it gets a little tougher, since customizing is a big part of Mini culture, but very nice cars are still available in the U.S., Canada, Australia, New Zealand and Great Britain.
Good luck with your search. Mini folks are great fun. If you get the time, there are 3 big Mini gatherings in North America this year: Spring Thing in St Petersburg, FL 3/7-3/9; Mini Meet East in Montreal 7/1-7/4; Mini Meet West in Victoria, BC 8/11-8/15. All the shows should get over 100 classic Minis and a few dozen new MINIS along with attendees from all over N. America. There are almost certain to be a few Brits at each of the shows and possibly some Australians, Germans, and other enthusiasts from around the world.
Like someone else said, check out Mini Mania's classified ads and discussion board. It's almost exclusively devoted to the classic Mini, and about 2/3 of the members are from N. America.