It isn't always easy finding information about "our" Wesley Dennis on the internet. Most of what turns up on search engines are sites selling Marguerite Henry books or recordings of the country music artist! But there are a few that I've been able to ferret out:
Wesley Dennis at the National Sporting Library
Illustrations at the University of Virginia
UVa Press Release about the Misty of
Chincoteague Collection
Misty of Chincoteague Foundation
Kerlan Collection at the University
of Minnesota