http://www.runningpast.com/vintage_media.htmhas a bunch.
http://www.mines.edu/Outreach/k12/mathcamp/BillyMills.show.htmlused to have the last lap of the '64 Oly 10k (Billy Mills) but is a dead link now. Don't know if it's still up anywhere.
http://www.kingofthemile.com/videos.htmlhas El G.
http://groups.msn.com/TheExtraMile/videofiles.msnwhas some stuff
http://www.ryunrunning.com/has Jim Ryun
and there's plenty more on the net if you want sprints, hurdles, throws, etc.
As far as VHS or DVD goes, here's a list of the best:
Olympia (
http://www.runningmovies.com/o.htm#154)
Invented the sports documentary as we know it.
The Olympiad Greatest Moments (
http://www.runningmovies.com/o.htm#156)
8-video collection of Bud Greenspan's documentaries. One tape has all the 800m and 1500m finals, another all the marathons, etc.
Tokyo Olympiad (
http://www.runningmovies.com/month2004.htm#January)
Another great documentary.
The Supermilers (
http://www.runningmovies.com/month2004.htm#April)
World record races. Difficult to find but well worth it.
Fire on the Track (
http://www.runningmovies.com/month.htm#January)
Prefontaine footage.
Also keep your eyes peeled to ESPN Classic's "Classic Sports Spectacular". They have a small number of shows they repeat and one of them is called "The Long-Distance Runner", with the Dream Miles, a few Pre races, and so forth. A great hour of 70s track!