I bought from Holderread's several years ago (Khaki Campbells). They are wonderful birds, still healthy and beautiful. He isn't that much more expensive than anyone else. I wouldn't worry too much about buying locally for 4H shows, but I'm not so much about kids doing everything there is to win, it's enough that they learn the ropes, have a good time and make friends. If your kids find they really enjoy it, they can learn to breed up their stock (if need be) or get something fancier later. If I had a 4H kid and there was drama about competing against the person they got their livestock from, heads would roll!
To me, personally, that would be unacceptable behavior in an organization where they are to learn how to do things and general good sportsmanship.
I did my share of showing in the dog world and I really despise the nastiness that people get in to when winning becomes everything. It was a shock to me when I started to do well at the higher levels the amount of lying, back biting, lawsuits over nothing, broken words and competition to sell pups or stud services. I was pretty sheltered I guess, that sort of thing was never allowed in our family and I showed with my mother until I was in my early 40's and I lost her to cancer. We had a wonderful time, win or lose.
These are just my thoughts, I do recommend Holderread's for nice birds. The back two are Welsh Harlequin, the front three Khaki Campbells, all from Holderreads. BTW, I'd recommend the Welsh Harlequins over the Khaki Campbells, they lay as well and are calmer, a little bigger and prettier. It is a little harder to get the color and some of the big hatcheries seem to send out birds that aren't clearly the right breed.