cannot find keytool on a mac

To answer the original question, on my Mac, keytool is found at /Library/Java/JavaVirtualMachines/jdk1.7.0_45.jdk/Contents/Home/bin/keytool.

You can locate the Java home directory using the /usr/libexec/java_home command line tool on Mac OS X 10.5 or later.

If you already have android studio installed, then keytool is located at

/Applications/Android\ Studio.app/Contents/jre/jdk/Contents/Home/bin/keytool

example to generate sha1 and sha256 using keytool

/Applications/Android\ Studio.app/Contents/jre/jdk/Contents/Home/bin/keytool -genkey -v -keystore ~/key.jks -keyalg RSA -keysize 2048 -validity 10000 -alias key

If you are using Eclipse under Mac OS X you just need to
Select File -> Export -> select Android -> Export Android Application -> click next -> select your project -> click next -> here you just chose Create new keystore

The actual tool should be installed all ready, as to my knowledge it ships with the MAC. You then have to create the .keystore file http://www.androiddevelopment.org/tag/keytool/ shows how to do it