Australia Citizens
Issuing Organization: Australian Federal Police(AFP)
Link: https://www.afp.gov.au/what-we-do/services/criminal-records/national-police-checks

Canada Citizens
Issuing Organization: RCMP
Link: http://www.rcmp-grc.gc.ca/

Ireland Citizens
Issuing Organization: Garda Síochána
Link: https://www.garda.ie/en/About-Us/Online-Services/Data-Protection-FOI-Police-Certificates/Police-Certificates.html

New Zealand Citizens
Issuing Organization: Ministry of Justice
Link: https://www.justice.govt.nz/criminal-records/get-your-own/

South Africa Citizens
Issuing Organization: South African Police Service (SAPS)
Link: https://www.saps.gov.za/services/applying_clearence_certificate.php

UK Citizens
Issuing Organization: mygov.scot
Link: https://www.mygov.scot/basic-disclosure/overview/

US Citizens
Issuing Organization: FBI (takes up to 3 months)
Link: https://www.fbi.gov/services/cjis/compact-council/national-fingerprint-based-background-checks-steps-for-success

Australia Citizens
Agency: Department of Foreign Affairs and Trade
Link: https://smartraveller.gov.au/services/legalising-documents/pages/default.aspx

Canada Citizens
Link: https://www.international.gc.ca/gac-amc/about-a_propos/services/authentication-authentification/apostille-convention.aspx?lang=eng

Ireland Citizens
Agency: Department of Foreign Affairs
Link: https://www.dfa.ie/travel/our-services/authenticating-documents/

New Zealand Citizens
Agency: Department of Internal Affairs
Link: https://www.dia.govt.nz/apostille

South Africa Citizens
Agency: Department of International Relations & Cooperation (DIRCO)
Link: https://www.dirco.gov.za/consular/legalisation.htm

UK Citizens
Agency: Foreign & Commonwealth Office (FCO)
Link: https://www.gov.uk/get-document-legalised

US Citizens
List of Legit agencies:
http://www.usauthentication.com/
https://www.uslegalization.com/
https://www.monumentvisa.com/
US Department of state (Takes longer)