I've never heard of any pre-vet scholarships, specifically. I think it would be hard to develop them because so many students *think* they want to go to vet school, but change their minds and so many others really want to go, but just can't make it in. Also, pre-vets are such a diverse group with so many different majors and experiences that it'd be hard to compare them against each other as they apply to undergrad.
I would advise just continuing to look for merit or specific activity based scholarships. I don't think a scholarship specifically labeled "pre-vet" is going to give you much of a leg-up when applying to vet school, but being able to say "I aced my way through college and have a 3.98 GPA plus I was a star on my school's field hockey team" might help.