"I never said anything about books," Remus chuckled. "I said to learn the theory. There are certainly people he could talk to for that. Or other methods if he's too impatient to sit and listen. For that matter, Aurors are supposed to be trained as dark wizard catchers. Can't fight what they don't understand. Get Ron to add it to one of his class' training sessions. I'd say he should have gotten it during his school years, but I suspect even the theory is a foreign concept in recent years.
"And, actually, I can see Sirius reading up on it." Remus might have been the bookish one of the group, but neither of his friends had ever balked at doing the work when necessary. "He might need the right incentive to do it, like becoming the youngest unregistered animagi ever, but he'd do it."
Watching his friend with sympathy, it was Remus' turn to reach over and touch Harry's hand lightly. "Maybe it's time to stop trying? Step back. Give him a hug and send him out into the world until he comes back of his own accord. You have to go grey eventually," he teased gently.