I'm doing a documentary on preparing a runner to break the 2-hour marathon mark. I have searched the websites of several cable channels (Discovery, History, Health) to establish their quality standards for footage (25, 50 Mbs? 4:2:2 color?), but haven't found anything.

How do I find out what their quality standards are?

There are HD spec sheets for various channels, these also list the formats they regard as standard definition for example.

http://dhd.discovery.com/guidelines/gallery/guidelines.pdf

These are the highest, other channels have other requirements,

Discovery HD Gold, Silver, Bronze tiers | In depth and practical guide to television production | eyefish.tv (http://eyefish.tv/production-guide/high-definition-production/broadcasters-requirements/discovery-hd-gold-silver-bronz)