They can be pushed from adb to your /system/fonts directory. If I find the info how to again, i will post it here.
But basically you find the font you like, have at least 2 of them named Droidsanserif.tff and droidserif.tff.
You push them from your pc via adb to /system/font dir
reboot.
They can sometimes be pulled out of themes, but I want to know how these theme builders are actually making them.