You say that you're about to start breeding the roaches...
Are you feeding them off to your chams yet? Because you only need to gutload insects when you are feeding them to your chams.
If you are just starting up a colony, and are not feeding them to your chams yet, then you don't have to be as fussy about the food you feed the roaches.
Just give them a steady supply of fresh veggies, and an occassional protein source. For the protein source you can use alfalfa pellets, or eggs, or milk powder, crushed nuts - they eat just about anything. All of those protein sources are healthier than fish or cat food, although these are recommended by some. If you have a supply of it, good commercial gutloads that are used for crickets are just as good for roaches.
Remember that gutloading is the process of getting insects to ingest nutrients (without complete digestion) that you wish to pass onto your cham via the feeder insect - it doesn't really have anything to do with the long term feeding of the insects.
If you are feeding the roaches to your chams, then you can gutload them in the same way that you gutload your crickets.