Todos os arquivos Simple.pm que você encontrou pertencem a outras bibliotecas Perl. Nenhum deles faz o que você quer. Você encontrou
IPC::System::Simple
Lintian::Command::Simple
Log::Message::Simple
Locale::Maketext::Simple
Pod::Simple
Test::Simple
Filter::Simple
Log::Message::Simple
Para encontrar o caminho certo, você deve fazer apt-cache search XML::Simple e escolher um pacote para instalar com sudo apt-get install <insert your choice> .
No meu Ubuntu 16.04 (YMMV), mostra-me:
$ apt-cache search XML::Simple
libxml-simple-perl - Perl module for reading and writing XML
libdns-zoneparse-perl - Perl extension for parsing and manipulating DNS Zone Files
libgtk2-gladexml-simple-perl - clean object-oriented perl interface to Gtk2::GladeXML
libtemplate-plugin-xml-perl - XML plugins for the Template Toolkit
libtest-xml-simple-perl - Perl testing framework for XML data
libxml-libxml-simple-perl - Perl module that uses the XML::LibXML parser for XML structures
libxml-opml-simplegen-perl - module for creating OPML using XML::Simple
libxml-simpleobject-enhanced-perl - Perl module which enhances libxml-simpleobject-perl
libxml-simpleobject-libxml-perl - Simple oo representation of an XML::LibXML DOM object
libxml-simpleobject-perl - Objectoriented Perl interface to a parsed XML::Parser tree
ruby-xml-simple - Simple Ruby API for reading and writing XML
libxml-hash-lx-perl - module to convert hash to xml and vice versa using LibXML
libxml-struct-perl - represent XML as data structure preserving element order
libxml-structured-perl - Convert XML data into a predefined Perl data structure and back