How do I build CWM or TWRP?

1.) Where do I find the TWRP and CWM source? All I could find is CyanogenMod/android_bootable_recovery on Github for CWM and omnirom/android_bootable_recovery on Github for TWRP, but these do not look like the official repositories.
2.) From what I can make out, the recovery partition must be built along with the custom ROM, rather than as a standalone thing. How do I set up the android source to build a different recovery source when "make recoveryimage" is run?