Motorcycle Competition

This is one from my childhood and could only have been found by a parent who knew dirt bikes. There are lots of other titles similar but this one would have been bypassed by someone looking for a glitzy book. It's a thin old publication, likely only on secondhand stalls now, but worth seeking out. There are sections on each discipline of proper motorcycle sport and includes a sub-section on USA specific sport. As the 1973 Bultaco Sherpa is an up-to-the minute competition bike, that dates the book around the mid-1970s, but still a worthwhile publication. It is hardback and 310mm x 230mm with 64 pages. Where do I get one? Scour auto jumbles...