http://www.linuxfromscratch.org/blfs/view/cvs/pst/docbook-xsl.html claims to have a link
You might be able to just download that from somewhere
And specify --with-xslroot=<path>
when configuring

brew install docbook-xsl

--with-xslroot=/usr/local/Cellar/docbook-xsl/1.79.2_1/docbook-xsl