The Pearson iGCSE has been around for many years, so you will find plenty of past papers to practice, yipee.
The Cambridge iGCSE is a newish qualification. There are only a few of its past papers released for public use.
The OXFORD/AQA iGCSE is a newish qualification. Unfortunately these past papers are not available to the public, so you will not be able to find these papers on the internet. However, OXFORD/AQA has made one set of specimen papers available for students to look at. These are available on the exam board's website.
Ensure you know your exam board - Pearson, Cambridge or Oxford/AQA. If you are unsure which exam board you will be sitting, ask a maths teacher at your school or college.
The lower tier
is
for those students aiming for a grade between 1 to 5.
Pearson
call this tier foundation.
Cambridge
call it core.
Oxford-AQA
also call it core.
The higher tier
is for those students aiming for a grade between 4 to
Pearson call this tier higher.
Oxford-AQA call it extension.
Cambridge call it extended.
Both of the lower teir and higher tier have their own unique syllabus. But also, some topic overlap. Typically, the harder end of any foundation paper contains the same questions as the start of its corresponding higher paper.
First, start by practicing past papers from your exam board of entry. This will enable you to become familiar with their unique questioning style. But yes, I would also recommend looking through and selecting some question to practice from other exam boards.