Anyone know where the powerpc iso for natty is? I found the one for oneiric -- http://cdimage.ubuntu.com/daily/current/ but there is not one for natty in http://cdimage.ubuntu.com/ports/releases/
There is no official PowerPC support in Ubuntu since 7.04.
Unofficial ports are made exclusively by volunteers, and always lag a bit behind. So I guess you just have to be patient.