Kindle Fonts hack can be found here:
https://www.mobileread.com/forums/sho...d.php?t=219405
Requires jailbreak, but it's pretty simple. Everything usage is handled through the KUAL launcher.
HOWEVER, this is very much a hack, so
here be dragons. That being said, lots of people have found a lot of success, assuming their custom font doesn't blow everything up.