W. Veech on Teichmüller curves in moduli space, Eisenstein series and applications to triangular billiards says on the second paragraph of page 579:
"Thurston's original construction [8] corresponds to the case $r=s=1$." In this context [8] refers to a preprint of Thurston. A reference to this preprint can be also found in Thurston's On the geometry and dynamics of diffeomorphisms of surfaces, where he begins by saying "This article was widely circulated as a preprint".
I'm looking for a reference / copy of this preprint. More precisely, for a reference of Thurston's contruction of pseudo-Anosov homeomorphisms using only two curves (which was later generalized to the case of multicurves.