This is actually a huge topic for aquaponics. How successful it is depends on the goals and space available. There is no single thing that can replace commercial fish food all by itself. Things like worms, BSF larva, maggots, duckweed, moringa, algae, spirulina etc are all hot topics but no single one is the answer all by itself.
The worms, BSF larva and maggots are probably all too fatty to be the only feed. Duckweed is great feed supplement but mainly for the fish that like their veggies and it takes a huge amount of duckweed to support say 100 tilapia. and so on.
Biggest problem is that if you are growing a large amount of fish you need a large amount of space to grow the feed and if you want to use automatic feeders you then need some way to make the feed into uniform pellets that will keep in the feeder for more than a day.
Now in a more low key aquaculture sense, it is fairly easy to fertilize a pond a little bit and grow a pretty good mixed population in a farm pond with just a little bit of management. If you are trying to do this in Aquaponics the balance is trickier since we feed the fish in order to get nutrients to grow the plants in the aquaponics system.
Bill Mollison does address techniques for growing food for animals in the Designers Manual, but there are few specific examples. The information in the manual does not leave us empty handed however, as there are several useful tools you can use to make sure you don't over stack system with to many animals. The ability to grow feed is not the problem. It is what you grow and whether it can sustain the population of livestock you have.
There are several methods of raising all manner of livestock utilising specific grazing patterns out there.
The problem with aquaponics is not the inability to grow enough feed. It is what to grow or raise and whether such a venture is viable.
I think the second question can be solved by forming regional feed cooperatives. The first is up to research.
I'd sure like to read that book! hint hint;)
Well at present I am working on this exact topic and will share my results at the end of this season.
I have been following your posts on the subject and I really look forward to what you come up with.