As the International Electrotechnical Commission - IEC - holds the copyright on the IEC 61131-3 standard we cannot provide a download version.
In case you cannot get the document through your local standardisation organisation, you can contact:
International Electrotechnical Commission: www.iec.ch
American National Standards Institute: www.ansi.org
British Standards Institution: www.bsi-global.com
Belgisch Elektrotechnisch Comité: www.ceb-bec.be
Standards Council of Canada: www.scc.ca
Deutsches Institut für Normung: www.din.de
Japanese Standards Association: www.jsa.or.jp
Nederlands Normalisatie Instituut: www.nen.nl
Electrosuisse Switzerland: www.electrosuisse.ch