What are Primary Sources?
A piece of evidence created by someone at the time of the event e.g. letters, diaries, original photos, autobiographies, artifacts etc.
Where to find them:
What are Secondary Sources?
Information created by someone who was not present at the time of the event, after the event happened e.g. Newspaper articles, textbooks, documentaries, biographies etc.
Where to find them:
For Excellence, you need to show "persevering with difficult sources, and/or using evidence from sources which are not readily available." Such as:
Government documents
Official reports
Where to find them:
To find difficult sources, you need to dig really deep across the internet. I can help you with this but it needs to be majority independent work.