The "National Stakes Conditions Book" by bloodhorse.com has all the USA races (you need all 4 to get all of the races across all quarters). There are select UK and JAP races in these books too but not all of them.
Australian stakes races are at this link
https://www.racingaustralia.horse/arb/Group_ListedRaceDates/2019-2020.aspx.
Japan is here (there's a PDF version too):
http://japanracing.jp/en/racing/schedule/graded/list/2020.html.
Can't find where I got the PDF of NZ races I found but it's for 17/18.
Other than that, there's Wikipedia (especially handy for things like the Road to the Kentucky Derby) or a race betting website with an international calendar.