The dutch calendar came from here:
http://forum.mokkels.nl/cgi-bin/groups.pl
and there were a few more. Click on Onbekende Mokkels, then find sports babes (maybe there, not sure) but its all in dutch. Anyway, great site and lots of vsoft (very soft - anything nude but no breast, butt or pussy) stuff.
I'll bet this is all just the tip of the iceberg for hidden nudity. My guess is there is a TON of retro stuff nobody has even begun to look for. And what about all the TV and film clips where they visit nudist resorts but can't show anything?
Gotta run,
KLondike