/usr/share/sgml/docbook/xsl-stylesheets-1.75.2/epub/bin/dbtoepub
/usr/share/sgml/docbook/xsl-stylesheets-1.75.2/epub/bin/lib
/usr/share/sgml/docbook/xsl-stylesheets-1.75.2/epub/bin/lib/docbook.rb
You may install this package on CentOS with
yum
install docbook-style-xsl