Why not just get the kinds you want? (Say 2 of one kind and 3 of the other since you said there is a 5 chick minimum.) That way if something were to happen to one, you would still have one or 2.
Am I correct in thinking that the store won;t have all of those breeds at once? If that is the case, I would just wait and see what else is available when the breeds you HAVE to have are in stock and go from there.