Smoky Mtn Knifeworks has some knives with hoof picks on them, so does Frost (owned by Jim Frost, who owns SMK), but the brand isn't particularly good, and I really wouldn't recommend them for any use, let alone hard use. If it's all your friend can afford, I would say go for it, but if he can afford more, I would say that they can look at a tack stores order books, they should at least have the option to get a hoof knife. Or, you can make the mistake I did, buy boat knives thinking they were hoof knives, when you were 15 as a gift for your sisters, only to be told by your dad that they are in fact boat knives. Oh well, at least my father and uncles like them, and use them on their boats...
Also, if your friend has not grown up around horses or has not handled them all his/her life, talk to the vet before they go playing around with a horses hoof. Y'know what, ask a farrier, they should know where to get the good stuff!