I'd look for started pullets, if you want to jump ahead to the laying part, since you already spent a lot of time raising these boys. I'd also look at how to tell the difference between pullets and cockerels (like the feather shape and growth, and colors) so you don't get some unscrupulous seller ripping you off. Some breeds are hard to tell even as they mature (like Silkies), but your males are very obviously male.
As far as what to do with them, hopefully your nephew will offer to take them back or have suggestions that would apply to you locally. Around here, there's a few farms that will take unwanted cockerels as dinner donations, or you may have a raptor rescue that would be happy for some meals for their charges. Or you can try putting up ads at your local feed store (one of mine kept a "rooster rehoming" list) and see if you can find them new homes, but depending on your area, that may be tough, if roosters are not allowed anywhere near you.