If someone came here decrying the lack of working ability in the border collies they have tried and then it turns out they were all from AKC "working" lines we would advise them to look for better dogs. I would offer the same advise here. If the dogs that have been tried on the ranch lacked the desired stamina; look for different working lines. Not everyone who breeds working dogs breeds to exactly the same criteria or the same goals. This is even true for those breeding for ranch dogs; they are breeding for their own goals colored by the work needed on their ranch which may not be what you need/want.
People need to give up this notion of the idyllic ranch bred dog; it is no more or less than a dog being breed to goals that were developed to meet the needs on that ranch (not all ranches and therefore ranch work is created equal).