At this stage your best source of past questions is the booklets you have been using as you worked through the course content. Most of these are available in Box accessed through the topic's relevant Firefly page.

Maths and Physics Tutor also has past questions by topic (click on this link).  Questions are shown as QP, answers as MS.

Cognito is an alternative to Physics and Maths Tutor.

If you really want some past paper practice clicking below is your best bet. The link also includes markschemes so you can check your answers.

AQA | GCSE | Combined Science: Trilogy | Assessment resources