there's a good calf stretch i know. you can even do it in front of a tree. you just need a surface to lean your arms against:
1. say it's your left calf that hurts. step close to but not against the tree.
put your right foot close to the tree. put your left foot behind you but not
too far. the Lt foot should be flat on the floor. with back straight lean into the
tree. you will feel your calf start to stretch. do this for about 10 seconds.
stretch only until you feel a slight pull. don't overstretch. if it's painful back
off the degree of stretch. repeat 2-3x's and you should have some relief.

hope this isn't too complicated.
you could also try one of those thermocare things that you can put on your
calf before you start a walk. that may help.

i get a lot of muscle tightness and heat is my best friend.
let me know if this helps.