Edexcel IGCSE

https://qualifications.pearson.com/en/support/support-topics/exams/exam-timetables.html

CIE IGCSE

https://www.cambridgeinternational.org/exam-administration/cambridge-exams-officers-guide/phase-1-preparation/timetabling-exams/exam-timetables/

Edexcel A-Level

https://qualifications.pearson.com/en/support/support-topics/exams/exam-timetables.html

AQA

https://www.aqa.org.uk/exams-administration/dates-and-timetables

OCR

https://www.ocr.org.uk/Images/670285-as-a-level-fsmq-and-level-3-certificate-core-maths.pdf

International Student ( outside the UK )

Simple Google Search IGCSE exam in your country or city, and you will find British Council has all the relevant information) see two examples below.
https://www.britishcouncil.org.bd/en/exam/igcse-school/register
https://saudiarabia.britishcouncil.org/en/exam/igcse-school