On what page of Guns, Germs, and Steel can the term "infrastructure" be found?
The word "infrastructure" does not appear in this book. However, there is at least one place in the book where infrastructure is discussed even if the actual word is not used.
The word "infrastructure" refers to the resources that we need in order to do some sort of activity. For example, we say that roads and bridges are infrastructure because we need them to be able to transport goods and people around the country. Diamond does discuss the infrastructure needed for farming in Chapter 6. There, on pages 110 and 111 in the paperback edition, he mentions that societies build up an infrastructure of things like underground storage pits. As they do so, they become more likely to adopt a purely agricultural way of life.
So, the word "infrastructure" does not appear in the book, but the concept does appear in Chapter 6.