The following are links which relate to walking in the Chilterns, that you might find useful:
This site lists the walks the author has taken between rail stations with descriptions and photos. Lots of ideas for walks here.
Nice idea of walks from the end of each Underground line.
The site aims to use the Underground network as a gateway to the countryside. Over 60 walks listed.
“A slowly growing collection of walking routes easily accessible by train from London”. Over 750km of walking routes listed.
A blog about walking with a large number of well illustrated walks.
A list of walks in Buckinghamshire.
Other useful sites