There are preloaded gut loaded critters out there, problem is that it doesn't stay in their bellies long. Most folks gut load theirs 24 hours before being fed, that way it has the highest nutritional value to your chameleon.
You don't have to breed, just feed your feeders.
Gutloading is better than nothing, but growing the insects on a nutritious diet right from the start, is better than gutloading.
For similar reasons, gutloading actively growing insects is superior to gutloading full grown adults.
The stuff they build their bodies out of really does effect them nutritionally- it isn't only a matter of what is in their gut at any given moment...
I only know of crickets that you can buy this way. I think LLLReptile sells vitabugs and that is what they are if I understand their advertising correctly. For some inexplicable reason they seem to have convinced the patent office that the process of feeding insects a highly nutritious diet as they grow is a unique concept or something. It isn't- it's been known for years. So it "bugs" me (pun intended) that they have taken a patent out on an idea that is a simple fact of life that they didn't even come up with. (unless I'm totally misunderstanding what they are doing)
But that is the only source I know of for buying reliably gutloaded bugs. That and someone selling soldier fly larvae is doing the same thing and advertising the difference in their specially fed maggots vs others (and they were doing this years before LLLReptile's patented vita bugs came out). I think it might repti-worms or calci-worms- not sure but their website has the data.
But the info on actually growing the bugs on a nutritious diet vs merely gutloading- that's been known for many years and has been published in years gone by.
On the other hand, although it maximizes nutritional value of the feeder insect to raise them on a nutritious diet from day1, you can get by just fine by simply gutloading.
If you do decide to buy the ones that have been fed a nutritionally enhancing diet, you still want to gutload them until they are fed off...